Hi Brian123,
The first place I would 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 … and perhaps more importantly know how and why to avoid the worst ones.
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 “comfort” and 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 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 (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists (based on all the parts of your personal value equation that are most important to you).
While I can’t speak to how a mattress will feel or how different mattresses will compare in terms of comfort and PPP for someone else … outside of PPP the most important part of the value of a mattress purchase is durability which is all about how long you will sleep well on a mattress. This is the part of your research that you can’t “feel” and assessing the durability and useful life of a mattress depends on knowing all the specifics of its design and construction and the type and quality of the materials inside it regardless of the name of the manufacturer on the label (or how a mattress feels in a showroom or when it is relatively new) so I would always make sure that you find out the information listed here so you can compare the materials and components to the quality/durability guidelines here to confirm that there are no lower quality materials or weak links in a mattress that would be a cause for concern relative to the durability and useful life of a mattress before making any purchase.
All the major brands (such as Sealy/Stearns & Foster, Simmons, and Serta) tend to use lower quality materials in their mattresses than most of their smaller competitors that will tend to soften or break down prematurely and I would avoid them completely along with any mattress where you aren’t able to find out the type and quality/durability of the materials inside it (see the guidelines here along with post #3 here and post #12 here and post #404 here).
Once you have reached 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