Hi Chimpskyx,
I generally leave the specific suggestions about mattress layering to the manufacturers (or retailers) themselves because they know much more about their mattresses and how every component and layer interacts together and with different people and they also have the benefit of a large database of customers which can act as a reference point. They also know about the smaller details of their mattresses and foam sources and the ILD’s of the materials they are currently using which can change from time to time.
There is no “formula” that can translate height/weight and seeping position stats into the most suitable layering because there are so many variables involved besides just the foam ILD itself (which is not exact). There are some general guidelines about different types of layering here, different heights and weights here, and different sleeping positions here but my goal is to provide more general guidelines and information that can help people have more meaningful conversations with the people who make and sell specific mattresses rather than to design a mattress based on specs alone … especially without a reference point of specific mattress that they have tested. For me to make specific recommendations on a mattress would involve knowing every detail of the foam sources that I was using, the type of ticking and quilting I was using in the mattress and how it performed with the layers under it, and a longer conversation on a phone call that would involve more information than just “stats” and latex ILD’s.
Having said that … S/M/F would be a “standard” recommendation for your wife and in the same 3x3 layering your side would probably be medium on top and then F/XF or something similar.
100% natural Dunlop is the same price as blended Talalay and you can mix the layers as you choose. If they were mixed … then generally the Talalay would be the top layer and the dunlop would be on the middle and bottom layers. It would be more of a preference of feel but you are correct that Dunlop has a higher compression modulus which means that it gets firmer faster with compression than Talalay and would feel firmer in the same ILD (although Dunlop even more than Talalay doesn’t come in “exact” ILD’s). This could be a benefit for those who either preferred the feel of Dunlop or who wanted a little extra support. The thickness of blended Talalay layers and Dunlop layers are slightly different so you would need the same type of layering on each side for the height on each side of the mattress to be the same.
The better options I’m aware of in the Central Virginia Charlottesville/Lynchburg/Waynesboro area are in post #3 here and there is a list centered around the Roanoke/Christiansburg area in post #5 here. These may not be in the same “value range” as what you are looking at so it would be up to each person and their personal “value equation” whether any better value available online and any options they provide for layer exchanges etc would “offset” the higher cost of a local purchase in your area. My general thoughts are that a 20% or so difference would be 'break even" in terms of the lower risk and “in person” service of a local manufacturer vs the possible better value and options (and of course good service as well) of a purchase from a better online manufacturer.
Phoenix