Hi tonster67,
The major brands such as Sealy/Stearns & Foster, Simmons, and Serta (including the Beautyrest Black line) all tend to use lower quality and less durable materials in their mattresses than most of their smaller competitors that will tend to soften or break down prematurely relative to the price you pay which is why I would generally suggest avoiding all of them completely (along with the major retailers that focus on them as well) regardless of how they may feel in a showroom 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).
Assuming that the materials in a mattress you are considering are durable enough for your body type and meet the durability guidelines here relative to your weight/BMI range … the choice between different types and combinations of materials and components or different types of mattresses are more of a preference and a budget choice than a “better/worse” choice (see this article). The best way to know which types of materials or mattresses or firmness levels you tend to prefer in very general terms will be based on your own local testing or your own personal experience.
I’m not sure what you’ve read since you found the site but the first place to 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 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.
Since your BMI is over 30 there is more information in post #3 here and the posts it links to that would be helpful for those that are in higher weight ranges or have a higher BMI and you would need to make sure that the materials and components in your mattress meet the durability guidelines I linked earlier in this reply relative to your BMI range.
While the process of how to choose a mattress would involve the same steps that are listed in the mattress shopping tutorial … most people in higher weight ranges or that have a higher BMI will generally need or prefer firmer mattresses (firmer materials will feel softer because you will sink into them more) and materials and components that are higher quality and more durable than those that are in lower weight or BMI ranges (the materials and components in a mattress will soften and break down faster for those in higher weight ranges than they will for someone that is in a lower weight range that doesn’t compress the mattress as much). I would be particularly cautious about mattresses that use more than “about an inch or so” of memory foam that is less than about 5 lb density or polyfoam that is less than about 2 lb density … particularly in the upper layers of the mattress (which are usually the weakest link in terms of the durability and useful life of a mattress).
If you let me know your city or zip code I’d certainly be happy to let you know about the better options or possibilities I’m aware of in your area.
Phoenix