For those of you that are having a little difficulty in finding the absolute perfect combination of pressure relief and support because of special circumstances, here are a few tips and tricks along the way that may help you along the way ... in no particular order. Don't forget that the forum is also a great place to ask your specific questions that you haven't found an answer for.
• If you are very athletic and broad shouldered or heavy chested (or both), a thicker softer comfort layer may be necessary to allow your shoulders to sink in enough. A zoned mattress with the shoulder and chest area being softer than the hip area may also be very beneficial.
• If you are a side sleeper and you measure the distance between the outside of a shoulder to the outside of the widest part of your chest under your armpit (especially in men) and the distance from the outside of your hips at their widest point and the outside of your waist at its narrowest point (especially in women), the largest of these two measurements may be a good starting point for the thickness of your comfort layer.
• For exclusive stomach sleepers, the thinnest possible layer that gives you pressure relief for the pointy Iliac crest of the pelvis (perhaps 1") with a firmer support layer underneath is usually best.
• If you are exclusively a back sleeper, then measuring the depth of the recessed lumbar area may be a good starting point for the thickness of your comfort layer. This can be easily measured by standing straight with your rear end and upper back lightly touching a wall and measuring the distance of the gap in your lumbar area.
• If you carry a lot of weight in your hips and/or have heavy/wide hips, especially with thinner shoulders, then a zoned mattress core that is firmer under your hips may be very helpful.
• If you carry a lot of weight around your middle, then a reverse zoned mattress core with softer areas under your hips and shoulders and a firmer area under your lumbar may help you sink in deeper into the mattress and allow the comfort layers in combination with the firmer support layer under your lumbar provide better lumbar support. This is almost always not necessary and may even be a real disadvantage for some body shapes and weight distributions. Be very careful before choosing a reverse zoning system of this type as this in combination with the resilience of some comfort layers it may lead to excess pressure on the lumbar which can be very sensitive to this.
• While it is not so readily available, be aware that softer latex in an ILD of around 14 - 19 can have similar pressure relieving qualities to softer memory foam. The concern of some manufacturers in using it is that latex in the softest ILD's will not last as long as firmer ILD's used in a comfort layer. While is may be true ... particularly in the case of all natural Talalay latex in the softest ILD's ... it is also important to realize that they will last longer than the equivalent softness of polyfoam or memory foam used instead so everything can be relative to what it's compared to. It may be a very good idea if you are using a very soft upper layer for pressure relief to consider using a topper with an appropriate material instead of having the same material as part of your mattress itself. This gives you great flexibility and allows you to replace the topper if it wears out faster than the rest of your mattress. Latex in the softer ILD's is generally not used as often as it could be in a mattresses while even softer poly foam (often under 10 ILD in the comfort layers) and memory foam (usually from 10 - 16 ILD) is used instead, both of which are not as durable as latex. having said this ... it's also very important to make sure that any soft materials in a mattress are not so soft and thick that you are risking good alignment.
• If you are looking for a "pillowtop" feel in a mattress, then soft foam over a firmer innerspring is the way to achieve this. Once again, latex in a soft ILD is your best choice here as it will certainly last longer than low or mid grade polyfoam in lower ILD's.
• A 2" comfort layer of softer foam over a support layer which is softer on top and firmer with compression (has a high support factor) will offer roughly the same pressure relief as 3" of softer foam with a very firm support layer under it.
• Support under the lumbar curve comes primarily either from the resilience and resistance of the comfort layer when you sink in deep enough for the recessed lumbar area to compress your comfort layer or from reverse zoning with a firmer zone under the lumbar curve and softer zones in the hips/pelvis and shoulders (instead of firmer under the hips/pelvis). This too is a method of allowing you to sink into your mattress more so the lumbar can compress the comfort layer which provides secondary support. Do not buy into the myth that a firmer support layer will support the lumbar curve as it may leave a gap there which has no support at all. It will only help hold up the hips/pelvis which certainly can help with alignment but not because it is supporting the lumbar curve ... it is supporting the hips/pelvis. Lumbar support and where it comes from is very commonly misunderstood and in the store may be wrongly "connected" with "firmer" mattress cores.
• Some latex ... particularly Talalay latex ... is tested for softness (ILD) using 6" of material while polyfoam is tested using 4" of material. This means that Talalay latex is rated as being firmer than its ILD would indicate. To roughly compare the ILD of latex with the ILD of polyfoam, add 20 - 25% to the polyfoam numbers. This is not completely accurate as there are many variables but it is more accurate than comparing them using the numbers as they are rated.
• Dunlop latex, especially those made in Asia or in some cases Europe, use metric numbers for their softness rating and this needs to be translated into the equivalent for other foams to make an accurate comparisons. The softest Dunlop is usually in the range of mid 20's ILD, no matter what the numbers appear to say although there are some Dunlop layers that are softer than this available.
• ILD is only one of 5 main factors, and often not even the most important one, that determines how pressure relieving or supportive a material is ... so be careful in using it alone in determining how well a foam material may perform in either role.
• Be aware that more than 3 zones in a mattress core are often an excuse to charge you more or more about "marketing" and are often unnecessary (although there are some cases where more zones can be helpful). Almost all zoned mattress cores only have 2 different firmnesses that alternate or go from firmer in the middle to softer on the ends and there is usually only a relatively small difference between zones. There is often no need for zoning at all and rarely is there a need for more zoning outside of having a firmer zone in the center under your hips/pelvis (typical 3 zone), a firmer layer under your lumbar curve with a softer layer under your hips and shoulders (reverse zoning which is also more common with 5 zones), or a softer layer under your chest and shoulders.
• Multiple thin layers of a thin material of the same ILD will tend to "act" softer than the same thickness of the same ILD in a single layer.
• Thin firm layers over thicker softer ones will tend to reduce the amount you sink into the thicker layer and produce a firmer less "in the mattress" feel at the slight expense of how exactly it will form a cradle and how deep you will sink in. It is a good technique where necessary.
• Progressive mattress constructions with more complex multiple layers can be more difficult to get right ... but can be more accurate, especially with the ability to choose different thicknesses of material as well as different ILD's. Differential constructions are easier to get right ... although they may not end up quite as "perfect" in every way.
• I would always keep in mind that while "theory" can be helpful ... it can also become overly complex with all the many combinations of materials and components that are possible and can lead to "information overwhelm" or "paralysis by analysis" and the only way to know for certain whether any mattress will be a good "match" for any specific person will be based on their own personal experience because "theory" is based on averages and not everyone fits inside the averages of a larger group of people that may otherwise seem similar.