Hi Terse,
Yes … you could replace the polyfoam with latex but you would also have a different mattress with a different "feel’ and performance that may be more or less suitable for your specific needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
I don’t recommend any specific mattress, materials, or design because there are too many variable and unknowns for “theory at a distance” to be more accurate than your own personal testing and experiences or to choose a single mattress out of all the thousands of different designs (see mattress firmness/comfort levels in post #2 here). The choice of different materials is based on individual preferences and of course on budget considerations. My “recommendations” are based on “how” to choose rather than “what” to choose and that no matter which materials you prefer that you make sure you know the quality of all the layers and components so that you can identify any weak links in the mattress in terms of durability and useful lifetime and can make more meaningful quality and value comparisons.
There are many people who like the “feel” of a relatively thin layer of memory foam over a layer of more resilient foam such as latex or polyfoam so that they have some of the surface feel of memory foam with the “feel” of a more resilient material that “comes through” the memory foam. There are also others (and I’m one of them) that like the “feel” of a relatively thin layer of latex over a layer of memory foam because there is a more resilient sleeping surface with some of the “feel” of memory foam that comes through the latex. Even the Tempurpedic Weightless collection has a design like this (a thinner layer of memory foam over a more resilient layer underneath it).
It’s certainly not an “idiotic” idea and all of these are perfectly valid designs as long as they are suitable for your specific needs and preferences in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences).
Phoenix