Hi Pamcguire1s,
The first place to start your research is the mattress shopping tutorial here (there is a longer and a shorter version) which has all the basic information, steps, and guidelines that can help you make the best possible choices … and know how and why to avoid the worst ones.
Post #3 here has more information about the additional considerations (more durable materials and firmer layers) that would also be important for those that are in higher weight ranges.
Two of the more important links in the tutorial that I would especially make sure you’ve read are post #2 here which has more about the different ways to buy a suitable mattress (either locally or online) that is the best “match” for you in terms of what I call PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks involved in each of them and post #13 here which has more about the most important parts of the “value” of a mattress purchase which can help you make more meaningful comparisons between mattresses in terms of suitability, durability, and value.
Once you’ve done some of the basic reading and are on step 3 and are ready to start testing some mattresses to confirm which types of mattresses and materials you tend to prefer then if you let me know your city or zip code I’d be happy to let you know about the better options or possibilities I’m aware of in your area.
Phoenix