Here is a brief list of the basic information and specifications you need to know about any mattress that you are seriously considering to make sure that it uses good quality materials and there are no weak links in the design in terms of durability. You can print this and take it to the store with you and show it to the salesperson you are dealing with to make sure ahead of time that they can provide you with all the information you will need to make an informed choice and/or you can ask them to only show you the mattresses they carry where this information is available. Better yet would be to call them or email them first to confirm that they will provide you with this information.
One of the most frustrating parts of mattress shopping can be spending time testing a mattress and finding out that you like it and it's a good match for you in terms of comfort, firmness, and PPP (Posture and alignment, Pressure relief, and Personal preferences) only to find out that the information you need to identify any lower quality and less durable materials that would be a potential weak link in the mattress or to be able to make meaningful comparisons to other mattresses isn't available and you've wasted the time you spent testing the mattress.
The information you need to know about any mattress you are considering (either locally or online) before making a purchase is ...
1. The type and thickness of all the layers or components in a mattress listed in order from the top down (or the bottom up) to make sure they add up to the thickness of the mattress.
2. The density of any polyfoam or memory foam layers (in lbs per cu. ft.).
3. The type (Dunlop or Talalay) and approximate blend (the percentage of natural rubber and synthetic rubber) of any latex layers.
4. The type of innerspring, the gauge of the coils, the number of the coils, and the density of any polyfoam edge support.
5. The type or blend of fabric and any quilting materials used in the cover. If the quilting material is polyfoam or memory foam and is in the range of "around an inch or so" or less then it's not essential to know the density. If any quilting layers are 2" or more then I would want to know the density of any foam materials in the quilting.
Once you have this information then you can compare it to the durability guidelines here to make sure there are no obvious weak links in the mattress that could compromise the durability and useful life of the mattress and to make more meaningful comparisons to other mattresses.