Hi nola,
Well two of these are similar (the only difference being the core) but the Nature is quite different from the other two and for most people would be much firmer particularly for side sleeping (the comfort layers are firmer overall and there is only 2" of 19 ILD before you start to compress firmer foam). It would probably help to know which positions each one felt the “best” or if you tested them all in all your sleeping positions or long enough to be able to really tell the difference between them. My tendency would be to think that 4" of 19 ILD latex would be a little on the thick/soft side for back sleeping but again it would depend on seeing your position when you were lying on it which of course I can’t do. I would make sure though that with the versions which used 4" of 19 that you were able to completely relax while you were lying on your back with no tendency to keep any of your muscles “tense” to hold your heavier parts up. I would also make sure that you spent enough time on your side on the nature to make sure that you felt no pressure points or joint pressure on your side. It’s quite possible of course that there is a wide range of mattresses that you would do well with and that you aren’t as sensitive to differences as some are (which can be a good thing :)).
As far as the specs go … when you are comparing polyfoam with latex … similar ILD’s in polyfoam will be firmer than latex because talalay latex is tested for ILD on a 6" layer for 25% compression (1.5") while polyfoam is tested for 25% compression on a 4" layer (1") and latex is also more elastic than polyfoam and will form itself to your shape better (more pressure relieving). Your preference for the firmness of the polyfoam core seems to indicate that you prefer firmer support layers but this may be to “offset” the thickness and the softness of the comfort layers.
While polyfoam in a support layer is not as subject to wear as it is in the upper layers … it also doesn’t have the same resilience and performance as latex. It’s “stiffer”, not as point elastic, and has a lower compression modulus which means it doesn’t adjust itself as well to different sleeping positions and weight distributions.
The coolness of a mattress will have more to do with the upper layers and the ticking/quilting than with the lower layers although they will have a smaller effect as well. In addition, any foam where you sink in more (like the 4" 19 ILD layers) will be a little warmer than the same foam that is a bit firmer and you don’t sink in quite as much although Talalay latex is cooler and more breathable than other foams. The polyfoam layer on the bottom is to help with the stability and handling of the mattress and to help protect the latex. PLB used to use this (an inch of polyfoam on the bottom) but people wanted “all latex” so they put an ultra ultra firm 50 ILD talalay latex on the bottom.
If you decide to order online, post #21 here has a list and brief description of the members of the site that specialize in helping people choose a mattress on the phone and shipping across the country. They are all somewhat different in their options and features but your testing will help them to help you decide on which of their constructions would work best for you. While none of them would be exactly like any of the mattresses you have tried, they are all good at “translating” your specs and experiences into the layering of their particular mattress that may work best for you.
Two of your mattresses in effect translate into very soft over very firm while the Nature translates into a more progressive construction similar to soft/medium/firm. Trying to match the ILD’s exactly without the layer thicknesses also being the same (which the online version aren’t) would involve approximation and intuition. I would try to decide on your favorite of the ones you’ve tested as a model.
The ticking on both the PLB and the Jamison are unquilted stretch knits which affect the feel of the latex underneath them less than a ticking which is quilted or a stiffer woven material.
The PLB probably has a little nicer ticking although they are both similar in terms of being a stretch knit. Both foundations are non flex but one is wood slats (PLB) and one is a metal grid (Jamison). Both would work well and I would rate them roughly equivalent in terms of performance.
While I have no idea what the guy meant about the foundation “performing” … I would guess he meant that it didn’t flex and he thinks a latex mattress should be on a more flexible foundation. While I don’t think this is the best choice for any foam mattress and most manufacturers would share this opinion … there are a few who do the same. I believe that a foam mattress does best on a rigid non flexing foundation so that the foam does all the work it’s designed to do. It could also be that the Southerland foundations cost them less and this may increase their profit but I certainly don’t know this for sure of course.
So overall … I would see if you can narrow down your choices between the three you mentioned (testing the two thicker comfort layers for alignment especially on your back and the Nature especially for pressure relief on your side). If they appeared to be equal … the “safer” choice would be the firmer thinner comfort layer of the Nature. When two options appear to be equal with careful testing in all your sleeping positions …I would always choose the firmer … either for purchase or as a guideline for an online purchase. If one of the 4" 19 ILD talalay models are clearly better for you in all your sleeping positions … then I would use the “best” of these as your guideline.
Phoenix