Hi connie,
The first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines that you will need to make the best possible choice … and know how and why to avoid the worst ones.
The industry has changed substantially since you last purchased a mattress and much of it isn’t for the better (see post #3 here and post #404 here).
I would particularly avoid the major brands which tend to use lower quality materials in their comfort layers which are a weak link in most of their mattresses (see the guidelines here). Even their “so called” latex mattresses have several inches of lower quality polyfoam in the top layers which will generally soften and break down long before the latex underneath and this can lead to the loss of comfort and support much too quickly (which isn’t covered by a warranty … see post #174 here).
There is also more about the factors that can affect the sleeping temperature of a mattress in post #2 here that can help you choose materials in your mattress that allow for more airflow and better temperature regulation and tend to sleep cooler.
When you get to step 3 in the tutorial then if you let me know our city or zip code I’d be happy to let you know about any of the better options or possibilities I’m aware of in your area.
Phoenix