Hi dogslife,
Given your overall weight, sleeping positions, and back issues … a softer comfort layer over a firm core as you prefer would be the best overall construction. Typically a side sleeper would need about 3" in the comfort layer and then go slightly up or down from there depending on the results of mattress testing regarding pressure relief and spinal alignment.
The two main materials you would be likely to consider in the comfort layers would be memory foam and latex. The first question I would ask about any mattress you were testing is to see a spec sheet or cutaway and to rule out any mattress that has more than an inch of polyfoam in the comfort layers unless you knew enough about the actual types and grades of polyfoam to know it was suitable for use in a comfort layer (this rules out almost all major manufacturers and almost all chain stores or typical outlets who will not have a clue about the specific types or specs of polyfoam such as ILD (also called IFD), Density, manufacturer, and compression modulus).
Memory foam and latex are roughly equal in pressure relief (if the latex is softer in the range of 19 ILD or less) however latex is much more durable, healthier, more breathable, and far more supportive (even in very soft versions) than memory foam and so is much more appropriate for back and alignment issues.
The firm support core could either be latex (more expensive in a support core but certainly the highest quality and most effective material) or firm polyfoam or a firm innerspring.
As you know from the responses here … local mattress manufacturers that sell factory direct or retail outlets that sell locally or regionally produced mattresses usually have the best value and certainly are the most knowledgeable and helpful in finding a mattress that is suitable for your own unique needs. Any mattress regardless of price, and sold in any store that will tell you the layer by layer construction of a mattress, makes a great testing ground … even if they are not the best place to actually make your purchase. If information about a specific mattress is available online (or through a question here) then it too may be worth testing as a “pointer” to the best type of layering for you, even if the store doesn’t know what is in it (or won’t tell you). When your mattress testing is done and you know the type and layering of a mattress that works for you … then you can purchase this mattress locally if it is available with good value or you can “duplicate it” through an online outlet if the value is better there.
There is a local manufacturer near you which would be worth going to see which is http://perfectlatexmattress.com/ if you wish to test latex mattresses in different variations.
Other than that there are no independent manufacturers near you that I am aware of however testing mattresses in local stores who will give you a layer by layer breakdown of what is in the mattress … and testing specifically for pressure relief and spinal alignment … will certainly give you enough information to know what to buy from an online “diy” manufacturer if this is your best source for the quality, construction, and value you are looking for. some of the better possibilities in the Roanoke area are in post #5 here
Answer about the adjustable base coming in the next post 
Phoenix