Hi tyiaone,
The PLB nature has …
2" of 19 ILD Talalay
1" of 28 ILD Talalay
6" of 36 ILD Talalay
1" of very high (@ 50) ILD Talalay
With a stretch knit cover
The Rocky Mountain 9" has …
2" of your choice of either 19, 28, or 32 ILD Talalay
6" of natural Dunlop (I don’t know the firmness but would guess it was in the “medium” range
cotton /wool cover.
These are very different mattresses and personal testing would really be the most accurate way to see which of the comfort layer options at RMM would be closest to your needs and preferences.
If you liked the Nature … you may also prefer the 2" of 19 ILD but how close this was to the Nature would depend on the ILD or density of the Dunlop support layer. Dunlop has a higher sag factor than Talalay which means that it can be softer with initial compression (and perhaps closer to the 1" 28 ILD talalay layer in the Nature) but gets firmer faster than Talalay (which means that even if it had a “softer” ILD it would quickly “catch up” to the firmness of the Nature support core as it compressed more).
If you were ordering online and using your experience with the Nature as a guideline … this is probably what I would suggest but this would be subject to knowing the density and firmness of the Dunlop. Your experience on the Nature could indicate that it may work well for your wife who is a stomach sleeper but that you may need a transition layer in between the softer comfort layer and the firmer Dunlop core (again depending on the firmness of the Dunlop) to make the transition from soft to firm a little more gradual for a heavier side sleeper. A firmer comfort layer (like the 28 ILD) would reduce the transition between the layers but may be a little too firm. There is a noticeable difference between 19 and 28. Of course your testing may discover that you prefer 28 over 19 in combination with the Dunlop because all the PLB mattresses use 19 ILD in the top layer and you may not have tried anything firmer. Each manufacturer though is much more familiar with all the details of their specific mattresses and have a broad range of feedback from customers that may have similar preferences and “stats” to you so I would put a lot of weight on any suggestions they have as well.
I personally would not try to “exactly translate” two mattresses that could be quite different except to the degree that liking the Nature says that you like softer comfort layers but not “really” soft like the Beautiful unless there were no other options. It also says that you like 2" of @ 19 ILD but in your case I would use your own testing on the RMM mattresses as the most “accurate” means of knowing which would be best for you if this mattress is the way you decide to go.
Post #2 here includes some of the other choices in the area of Hickory that may broaden your experience and options.
Phoenix