Hi Jonathan,
The first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines that can help you make the best possible choice that fits all your criteria … and perhaps more importantly know how and why to avoid the worst ones.
Post #3 here also includes more information about choosing a mattress for those that are in a higher weight range because you will need to pay even more attention to making sure that any mattress you purchase uses high quality and durable materials.
You can read a little more about memory foam and sex in post #2 here and there are many others that prefer more resilient materials for the same reason…
There is more about the different types and blends of latex in post #6 here but all latex is a high quality and durable material compared to other types of foam.
There is more about the many variables that can affect sleeping temperature in post #2 here but in very general terms latex is the most breathable and “coolest” of all the foam materials and memory foam tends to be the warmest. I would also keep in mind that the type of cover and quilting that is used in the mattress along with the type of mattress protector, any mattress pad, or the type of sheets and bedding you use can also have a significant effect on the sleeping temperature of a mattress regardless of the type of foam that is used in the mattress.
There is also more about how latex compares to memory foam in post #2 here.
This depends on the specifics of the mattress and the person sleeping on it so there is no way to quantify this specifically but there is more information about the many variables that can affect durability and the useful life of a mattress in post #4 here and the posts it links to. Latex in general though will soften and break down more slowly than other types of foam materials.
I would be very cautions about using reviews (either positive or negative) as a meaningful source of information see post #13 here.
When you see reports of “foam softening” with latex … outside of the very rare material defects that can happen from time to time … it’s usually the result of someone who chooses a mattress that was “on the edge” of being too soft for their body type and sleeping positions so that even a very small amount of foam softening that will happen with any material (less with latex than other types of foam) was enough to put them “over the edge” of the comfort and support range that was suitable for them or are the result of other layers in a mattress (besides the latex) that are lower density than would be suitable for someone’s body type (especially if they are in a higher than average weight range). These types of comments are almost always the result of making unsuitable firmness choice in the first place or the result of deeper layers that are lower density than would be suitable for the body type of a particular person rather than from any unusual latex softening. You can see more detailed comments about this in post #2 here.
As you can see in the previous posts I linked … this is usually true yes.
There is more about the different types of innersprings in this article and in post #10 here.
The better options or possibilities I’m aware of in the Atlanta area (subject to the guidelines here) are listed in post #2 here but you will need to check their websites or call them to see if any of them have a mattress on their floor which meets your specific criteria (I don’t keep a record of all the thousands of individual mattresses that are available at the manufacturers or retailers that are included in the hundreds of local lists in the forum which would be more than anyone could keep up with in a constantly changing market).
The tutorial post also includes a link to a list of the members of this site that sell mattresses online (in the optional online step) and some of these also make latex/innerspring hybrids. There are also some sources for latex/innerspring hybrids in post #2 here.
Phoenix