Hi Burgalicious,
The better possibilities I’m aware of in the Reno, NV area are listed in post #3 here. I would call them first to give them a sense of your criteria to make sure they carry something suitable on their floor for you to test.
With good quality memory foam (using 4 and 5 lb foams depending on the layering, your height/weight, and the suitability of your choice in terms of your needs and preferences) you should have no problem with your durability criteria.
The firmness level will vary from person to person (different peopl;e have a different sens of firmness … especially with memory foam) so personal testing will be the most accurate way to know how firm a mattress feels for you.
Memory foam is the least breathable of all the foams but there are many factors involved in the sleeping temperature of a mattress and for the most part, faster response memory foams are also more breathable. Some of the “pieces” of the puzzle of how warm a memory foam mattress may sleep for you are in post #6 here.
Some of the better online memory foam manufacturers or retailers that can either be a good source of better quality/value mattresses or can act as a “value” reference point for local choices are included in post #12 here.
Phoenix