Hi ryanc,
You are very close to the same area as Elkie and my comments and most of the outlets that are linked in post #4 here would probably apply to you as well.
There are some weight/height/body shape guidelines here and some sleeping position guidelines here but these are a starting point and your personal testing and experience for PPP (pressure relief, Posture and alignment, and Preferences) will be much more accurate than rough guidelines based on “averages”.
Both Tempurpedic and iComfort are not great value IMO but the gel memory foam that uses particles in the memory foam like the Serta are not as likely to be as durable in the long term as some of the better gel foams. Tempurpedic is very high priced compared to mattresses that use similar quality memory foam but at least it is known to have good durability.
In most cases … a mattress that helps someone with back pain is because it keeps them in good spinal alignment and this is individual to each person and their height/weight/body shape and sleeping positions. In other words … a mattress that helps one person with back pain can cause back pain in another. There is no such thing as a mattress that is “good for back pain” … only mattresses that help with pressure relief and alignment for each individual. Each person can interact differently with a mattress than someone else which is why someone who is knowledgeable and “skilled” in the art and science of mattresses can be your best friend in making your best choice.
Ashley Sleep does make some memory foam and some “partly latex” mattresses. Their latex mattresses have only thin somewhat meaningless layers of latex in between upper layers of polyfoam of unknown density and the lower polyfoam support core. Their memory foam mattresses include layers of very low quality memory foam (less than 4 lbs) and I wouldn’t consider them.
Hope this helps and if you have any other questions along the way … feel free to post them.
Phoenix