Hi Jules,
I don’t believe your layers from Ultimate Sleep are Talalay latex (see post #4 here) so at least two of your layers are “unknown” layers (although they are probably 20% natural/80% synthetic continuous pour Dunlop) but hopefully the ILD’s are “in the ballpark”.
If your pain was from pressure I would normally have expected that the pain would increase or would take less time to become apparent with firmer layers but it seems that your pain took longer with firmer layers so this may be “pointing to” layering that is too soft and affecting your alignment.
You can see some comments about DIY mattresses in option #3 in post #15 here and I would normally take a “bottom up” approach with a DIY mattress (see post #2 here) so sleeping on the two firmer layers to start with sounds like a good idea to me.
What kind of mattress pad are you using? A mattress pad can interfere with the ability of the latex to contour to your body shape and in some cases can reduce the ability of the latex to relieve pressure even though the mattress pad itself may provide a softer “surface feel”.
I personally wouldn’t make any additional purchases until you have some clarity about the types of changes that have the best odds of success and you have done some more methodical testing on some different combinations over the course of the night and compared the “symptoms” you experience on each of them because the only way to know whether any combination of layers will work for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) will be based on your own personal testing and sleeping experience.
Phoenix