Hi MeDave.
I am sorry to hear about your lower back pains.
The trend in the industry for the past 15 years has been designing mattresses that are using comfort foams (memory foam variants and/or newer “age” polyfoams) over a 6" - 7" High Density polyurethane foam support layer. Polyfoam prices vary widely depending on the polyfoam grade. The Polyfoam grade is measured by its density and by its “support factor” or progressive resistance to compression. There are 3 grades of poly foams from the lowest to the highest: Regular conventional (lowest grade), High Density (HD), and High Resilience (HR).
The HD polyurethane foam is commonly used as the very top comfort layer over other higher quality foams used in comfort layers because it is more resilient than Memory Foam and it can be made to be very soft and it is inexpensive to manufacture having a lower cost/inch than other comfort foams. Manufacturers that use lower grades of poly in thicknesses higher than 1.5" in a mattress are usually looking to higher profits … at the expense of long-term suitability, durability and customer satisfaction.
It appears that some of your conclusions are the reverse of the basis for the design. Memory foam does not provide better support than other foams, in fact, it is not found in the support layer of a mattress as it lacks supportive qualities; it is formulated and engineered for comfort more than support. The highest performing mattress support systems are either Latex foam, pocketed coils, pocketed coil/latex combinations or responsive polyurethane with densities 2.0 lb. or higher. Many mattress manufacturers have gone to a hybrid pocketed coil/comfort foam design to achieve balanced support and comfort needs sought by consumers.
I would strongly recommend that you start your research with 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. 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 “comfort”, firmness, and PPP (Posture and alignment, Pressure relief, and your own 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 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 (how well you will sleep), durability (how long you will sleep well), and the overall value of a mattress compared to your other finalists based on all the parts of your personal value equation that are most important to you (including the price of course and the options you have available after a purchase if your choice doesn’t turn out as well as you hoped for).
You may wish to peruse some of our Trusted Members here who manufacture high quality mattress products and have the material combinations you seem to be interested in.
Please feel free to come back for any questions you may have once you’ve had the chance to review the information listed above, and perhaps do a forum search to see if any of the mattresses you are interested in are discussed on our forum.
Phoenix