Hi jwilliams34,
The first place I would start is the tutorial post here which has all the basic information, steps, and guidelines you will need that can help you make the best possible choices … and know how and why to avoid the worst ones.
I would tend to avoid paying too much attention to reviews which can be one of the worst ways to choose a mattress that is suitable for you (see post #13 here).
Post #3 here and the posts it links to has more information that will be helpful for those that are in higher weight ranges.
Simmons and the other major brands tend to use lower quality materials in their mattresses so your mattress is probably well past its due date. I think the odds are high that a new mattress that is more suitable for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) will make a big difference (assuming you have no pre-existing back issues).
I would tend to avoid all the major brands (including Tempurpedic) and the tutorial post includes a link to some of the better online memory foam options I’m aware of that use similar or better quality materials than Tempurpedic at significantly lower costs (including Selectabed which makes the Tri-Pedic). You can see some of my thoughts about Rick and Relief Mart (who makes the Tri-Pedic) in post #9 here.
You can see some of the “quality” guidelines I would use in post #4 here. Other than focusing more on higher quality more durable materials though (such as 5 lb or higher memory foam or 2 lb or higher polyfoam, or latex in comfort layers especially) … I would avoid any preconceptions about what may work best for you or trying to design your own mattress ahead of time without a specific frame of reference because there are too many unknowns, variables, and personal preferences involved to choose a mattress based on specs or “theory at a distance” that don’t have anything to do with the quality of the materials (such as layer thickness). I would focus on either your own careful and objective personal testing (using the testing guidelines in the tutorial post) with a local choice or more detailed conversations with an online provider if you are looking in that direction (see mattress firmness/comfort levels in post #2 here).
When you are at step 3 in the tutorial … I’d be happy to let you know of any of the better options or possibilities I’m aware of in your area if you let me know your city or zip code.
Phoenix