Hi jjp603,
The best 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.
As you can see in the guidelines here … I would avoid both Sealy and Simmons mattresses or any mattress where you aren’t able to confirm the quality and durability of the materials inside it no matter how they may feel in a showroom.
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 (or that doesn’t feel as close to another mattress as you hoped it would) 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.
Needless to say … I would avoid both of the mattresses you are considering.
Phoenix