Hi SOFTMATTRESS,
The first place to start your research is the mattress shopping tutorial here which includes all the basic information, steps, and guidelines you will need to make the best possible choice … and perhaps more importantly know how and why to avoid the worst ones (including the major brands like Sealy, Simmons, Serta, and Tempurpedic or any mattress where you aren’t able to find out the type and quality of the materials inside it … see the guidelines here).
You are the only one that can feel what you feel on a mattress and there are too many unknowns, variables, and personal preferences involved to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or combination of materials and components would be the best “match” for you in terms of PPP based on specs (either yours or a mattress) or “theory at a distance” that can possibly be more accurate than your own careful testing or personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
Two of the most 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 choose a suitable mattress (either locally or online) that is the best “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) that can help you assess and minimize the risks of making a choice that doesn’t turn out as well as you hoped for once you sleep on it at home that are 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 quality/value comparisons between mattresses in terms of suitability, durability, and value.
Once you reach step 3 in the tutorial if you let me know your 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