Hi danielrhall,
Thanks for the kind words
The first thing I would probably do is confirm whether the topper you have is the all natural (100% natural latex) or the natural (blended latex) version. Almost all of the PLB toppers are either the natural version (which uses blended latex) or the Active fusion fast response(with phase change gel) version. If it is really "all natural" talalay then it would probably be N1 which could be anywhere from 14 ILD to 20 ILD (it's not as consistent as the blended) and in ILD's that were this low would probably also be less durable than the blended Talalay.
I think that a 3" 14 ILD topper (blended) or N1 (100% natural) of almost any material would be fairly risky for someone of your weight and would probably be more suitable for your lighter wife. This would depend to some degree on your weight distribution and body profile which will determine how evenly you sink into a mattress. Some people also have a wider acceptable range of spinal alignment before they will notice both short and long term "symptoms" of sleeping out of alignment. A softer thicker topper will also be less durable with your higher weight .... even with blended latex and especially with 100% natural latex and many manufacturers would hesitate to use it (especially in combination with other soft materials) for someone who was heavier. Many aren't even comfortable with 19 ILD for higher weights ... especially with thicker layers because the softening of a thicker layer will have a bigger effect.
In any case ... from your preferences it's clear as you mentioned that you prefer softer mattresses and if you are confident that you aren't risking alignment issues then it may still be OK. I would make certain that you have tested for alignment though because alignment is not as easy to "feel" in a showroom (some suggestions for testing for alignment are in
post #11 here
).
I don't know the details of the Pranasleep mattresses because they all use fairly thick polyfoam quilting layers on top of the latex (I don't know the specs of the polyfoam they use) which will add some softness to any latex that they use regardless of ILD.
As far as I know ... the old PLB Nature uses 2" of 19 ILD over a 1" 28 ILD. In the new models ... the 1" layer is now 2" and the top layer is now Active Fusion fast response and the closest ILD to 19 ILD in this material would be 21 ILD which along with the thicker middle layer would likely produce a similar feel but I don't know that for certain.
The "old" beautiful (again according to specs listed online) had 3" of 19 ILD and 2" of 24 ILD (which would be replaced by the Active Fusion fast response on top and an extra inch in the middle layer).
The World's best bed has the same overall thickness as the Beautiful but has an extra inch of the softest material in the top layer and an inch less in the middle slightly firmer layer.
I would be tempted to test the Pamper (which has 2" of Active Fusion fast response on top which I would also assume is 21 ILD) with their 3" topper on top of it to see how well that worked for you. If it worked ... then you would have some sense of how your topper would feel on a firmer mattress although even the Pamper has 2" of soft latex on top. I believe the Pamper used 40 ILD base foam (which is firmer than the other models and probably firmer than the ultimate Dreams as well).
The challenge for your higher weight with adding a 3" topper that is that soft is that it's difficult to predict how much you will "go through" it and feel any firmer layers below it. In the case of the Ultimate Dreams ... what you feel would depend on how much you "go through" the topper and the quilting layer combined and feel your choice of latex below this. The support layer is also polyfoam and probably doesn't "match" the latex support layers of the PLB. The 1.5" quilting layer in the Ultimate Dreams would lower the effective ILD of the top layers compared to what the ILD of the latex itself would indicate.
So all in all ... matching your topper/mattress combination to what you have tested would be more of an apples to oranges comparison with so many variables that you would be guessing more than anything else. I personally would tend to talk with Chuck about it (he will know more about how a very soft 3" topper may feel on the various choices and how much the quilting foam may affect this) but I would tend towards a fairly firm choice in the range of at least 32 and possibly higher because you are really choosing a transition layer between the comfort layers (your topper and the quilting foam) and the firmer support layer rather than a comfort layer itself which is what people would be choosing if they were going to sleep directly on the mattress itself. You will feel more of the latex layer ILD you choose than your wife because of your higher weight (she won't "go through" the topper and the quilting foam as much if at all). Generally a mattress would be chosen before a topper and the topper would be chosen to fine tune the mattress based on how close it was to your pressure relief and alignment needs.
I wish I could be more accurate but unfortunately there are too many variables to do much more than guess.
Phoenix