Hi emc.
Thanks for your kind words, I appreciate it!
Everyone is different … body types, sensitivities, support & comfort needs, and much more. Your prone sleeping position is also throwing a wrench in the works with more or less “extreme” support needs, but I am glad that you are getting some “problem improvement”.
It’s nice to see you so hopeful but don’t think we are yet done. We still need to meet like this for a while 
Before you move to the next step it would be good to clarify a few things so that I can further offer some comments. What was the exact layering (including the base) you used when you noticed the improvement? How many days into the “improvement” are you? Is it still holding on? Any other variations that you combined with the base “improvement” layout and the results for each.
I don’t doubt that. The coils are quite supportive but probably not supportive enough for you in the prone sleeping position.
It depends! I am assuming from your brief description that sleeping on the coils themselves has helped to alleviate some of your pain. I cannot tell from your “improvement” description if this unit would be supportive enough for you. Support should be your primary concern as it is not possible to fix if you get it wrong. The most important goal of a suitable mattress is to support the spine and joints in neutral alignment in all your sleeping positions so that the muscles and other tissues can fully relax and not work during the night to maintain good alignment.
Part of the challenge you may have is if the issue is lack of primary support (see post #4 for primary support, secondary support, and pressure relief and how they are related). Any attempt to “fix” support layers that are too soft by adding layers on top will often only be partially or temporarily successful because it would be more of a “band-aid” than a solution that “fixed” the core problem because the top layers can still “bend into” the support layers below them and lead to alignment issues. This is why I suggested you hold on with purchasing any comfort layers and asked some questions that may help determine if the coils are supportive enough for you.
Your secondary point of focus is to get enough softness on the surface to allow your pressure points to sink in enough so that direct pressure on various parts of the body don’t cause soreness. Too much firmness or too much softness in either the comfort or support layers can both lead to alignment and pressure issues, discomfort, or pain in various areas of the body.
FYI …there is also more about the more common symptoms that many people may experience on a mattress and some of the underlying causes that may be involved in post #2 here and the posts it links to that may help with some of the detective work or trial and error that may be involved in solving the symptoms you are experiencing.
In parallel with this, I’d do a bit of research and perhaps try some other comfort materials since it seems latex isn’t working for you. I’d consider looking into natural materials (featherbeds, wool, cotton, etc.) vs foams.
There’s more detail about featherbeds in this post and more about wool mattress pads and toppers with some sources in post #3 here. Also look inpost #8 here.
I would start here and see how a natural option would meet your needs. “Firmness” in the world of mattresses varies depending on the material you’re considering, as well as your only personal interpretation of how the mattress feels when you lay on it.
Looking forward to your continued updates.
Phoenix