Hi color,
The first place I would start your research in the mattress shopping tutorial here which has all the basic information, steps, and guidelines that can help with how to make the best possible choice for you … and can help you know how and why to avoid the worst ones as well (including Simmons or any of the major brands).
There is also more in post #13 here about the most important parts of the “value” of a mattress purchase that can help you make more meaningful comparisons between mattresses.
The tutorial post includes several links to lists of the better online options I’m aware of and if you can let me know your city or zip code I’d be happy to let you know about the local options or possibilities I’m aware of that may also be worth considering.
Phoenix