How to build my mattress

I am 5’3", 180 lbs. 76 years. I fell off my horse onto my lower back a few times and am paying for it now. I am sleeping on a good quality hide-a-bed with a sheet of plywood on the mattress because of the uncomfortable bar on the frame. It is like the floor. I added 4" of firm poly foam, then memory foam which was OK for awhile until it failed and I was feeling the poly and the pain really started. My last try for relief was to research latex and purchase a 2" soft telahay topper. After a few weeks I realized that I was feeling the firm Poly layers and that they were giving out. I am looking to build a mattress in layers no thicker than 3", which I can move in the future. I like a soft feel and sleep mostly on my side. I don’t have the padding over my bones that I use to, so firm is not comfortable. I was told that I need 6" under the 2" I already have. What say you?

Hello Mstanya

Thank you very kindly for your inquiry. I appreciate all the info you have provided. It makes it easier to recommend a layer configuration that is right for you.
Based in your information, I would suggest placing your 2" soft Talalay over a 3" Medium Talalay over a 3" Medium Dunlop layer. At 180lbs, the soft on top will provide the contour you need, while the medium over firm layers below will provide the gradual support.
Talalay is just a bit softer and slightly more contouring than that of the Dunlop latex, and this is why I suggest the second layer to be medium Talalay. I think based on your pressure point issues, choosing Talalay latex for both the top layer and the second layer will be ideal for you. I recommended the third layer as a Dunlop firm so that you can have a nice solid support layer at the bottom. This will prevent you from sleeping in the mattress as opposed to on it.
Please keep us posted as to what you decide to do. Let us know if you have further questions. Have a terrific weekend!