Hi ihavezippers,
I think the first thing I would suggest is to read post #1 here and the links it includes.
I think you could be making a few assumptions that may not be accurate.
Any type of materials can provide you with pressure relief and alignment in the right layering combinations although it’s certainly true that different materials will certainly feel and perform differently and your preferences may lean towards some over others. All mattresses are a combination of softness on top (for pressure relief) and firmness underneath (for support) and the key is always to find the best possible balance regardless of which materials you choose for either the comfort layers or the support layers.
Your back issues may have nothing to do with whether any memory foam mattress could work for you and may only mean that the specific one you are sleeping on has either softened too much to keep you and your wife in good alignment (which is most likely) or that your needs have changed and the specific layering of the mattress you have is not the best for you any more. A mattress with different layers of memory foam on top and/or a different firmness level of polyfoam underneath the memory foam than what you have may still work very well for you.
Memory foam is also completely different from latex (almost it’s opposite) and latex may also be a good option regardless of whether a certain memory foam layering is what you need or prefer.
An innerspring is only a support layer and provides deep support just like a polyfoam support layer (which is what you currently have) or a latex support layer. There are hundreds or thousands of “innerspring” mattresses that may use memory foam, polyfoam, or latex in the comfort layers and while one type of innerspring with a certain combination of comfort layers over the innerspring may work very well, another type of innerspring mattress with different comfort layers over it may be worse than your current mattress.
So there are hundreds of different mattresses that use different combinations of memory foam, latex, or polyfoam in their comfort layers and many different types or either innerspring, polyfoam, or latex support cores and any of these combinations can include mattresses that work well for your specific needs and preferences and others that don’t and lead to either pressure relief or alignment issues.
In other words … innersprings are not really really a “type of mattress” as much as they are a type of support component that can use any type of comfort layer over them and it may be the thickness/softness of your comfort layers or the fact that they have softened too much that are the real issue … not the type of support layer that is under them.
So regardless of the specific types of components you may choose … it’s always the balance between the firmness of the support layers and the softness/thickness of the comfort layers that provide you with what I call PPP (Pressure relief, Posture and alignment, and Personal preferences) that would help you sleep in better alignment and alleviate the “symptoms” of sleeping on a mattress that has either softened and degraded too much or that doesn’t have the best layering combination for your current needs.
If you do choose to use an innerspring in your support layers (as a preference) instead of other equally supportive materials … then each retailer will normally provide information about the type of innerspring, coil count or gauge of wire that they use although almost all innersprings used in reasonable quality mattresses mad today are not the “weak link” of a mattress (the layers that soften or degrade the fastest and that are the biggest reason a mattress needs to be replaced). The weak link is usually in the upper comfort layers as I suspect is the case with your current mattress.
I should also mention that coil counting though is among the worst ways to buy a mattress as you can see in the overview about innersprings here.
So I would “undo” some of your thoughts about which type of mattress may work best for you and start at the beginning again. I would first do a bit of preliminary reading about mattress materials and construction that are linked in the post I mentioned which can give you some good information about the most important parts of choosing a mattress. The next step would be to identify some of the better manufacturers or retailers in your area where you can test different types of mattresses to see which material combinations you prefer and work with someone that can give you accurate information about their mattresses and that has the experience and knowledge to help you choose a mattress that best fits your needs and preferences. This will let you test the differences between different types of material combinations. In essence … what you are looking for is a support layer that keeps you in alignment, comfort layers that relieve pressure, materials and components that provide the preferences that are most important to you, and the best possible quality/durability in each type of material that your budget allows.
If you let me know the city or zip where you live I’d be happy to let you know of any better manufacturers or retailers or at least “possibilities” that I know of in your area.
Phoenix