Hi Jeff Bennett,
The first thing I would suggest is to read post #1 here and the information and guidelines it links to. This will help you eliminate some of your options (the major brands like Serta) and focus on your better options.
A mattress is only as good as the construction and quality of the layers and materials that are inside it so the next step is to make sure that the retailer you are considering can provide you with the quality specs of every layer in their mattress. This means that for the Restonic you would need to know what is in the 3" quilting layer, the density of the 1" polyfoam layer, and the type of latex they use (probably blended Talalay which is good quality but I would want to confirm this). If they can provide this then you have a way to make a meaningful assessment of the relative quality and value of the mattress and to see if it has any potential weak links in terms of durability. Weak links will typically be in the upper layers of the mattress. If you can’t find this information either from US-Mattress or in your online research (if you are willing to spend the time an effort to find wat the retailer should be providing you) then I would pass this one by as well.
In an apples to apples comparison with similar quality materials … a double sided mattress is certainly a durability bonus. There are many single sided mattresses as well though that use high quality materials in the top layers (such as latex, HR polyfoam, or high quality memory foam) that are also very durable. The problem with durability in most cases is not the design so much (although this can certainly have an effect) as the quality of the materials in the upper layers. A single sided mattress has the advantage of having more design flexibility because you can layer softer foams on top (using higher quality materials) without taking the risk of affecting support when a thicker and softer top layer is part of the support system on the bottom of the mattress.
Original Mattress is a regional factory direct manufacturer which makes some good quality and value mattresses and they are fully transparent about the materials inside them. I would certainly consider them as a potential choice if they had an outlet in the area. Even here though … they use 1.8 lb polyfoam in the comfort layers (which is a better quality material than the major manufacturers typically use) and if these are too thick and soft then they can also suffer from sagging and impressions and I would tend towards the thinnest possible comfort layers that provide you with the pressure relief you need without going any thicker than you need to. I would avoid the temptation to choose a mattress that is softer than your body type, sleeping positions, and preferences indicate you really need. They also don’t have a retail location in the Memphis area so their mattresses would incur substantial additional shipping charges and you would be taking the risk of buying a mattress that you hadn’t personally tested. They may not be the best source for an online mattress purchase and you would have little recourse available at a reasonable cost if you made the wrong choice for your comfort or support needs.
Some of the better options or at least possibilities in the Memphis area are listed in post #2 here.
Phoenix