Hi JP314,
Lower back issues are most commonly from comfort layers that are too thick and soft or support layers that are too soft (see post #2 here) which can lead to the pelvis sinking down too far relative to the other parts of the body but each person is unique and just like with any type of back issues there can be many causes for the same type of “symptom”. Any health professional will confirm that back issues can be amazingly complex and it can be difficult to accurately “diagnose” the source or underlying cause of any specific symptoms you are having. The type of material is more a matter of preference and any type of mattress can be made in a design that is suitable for some people in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) and not for others. In other words the design of the mattress is more important than the type of materials.
I would also think in terms of spinal alignment rather than support because both a soft and firm mattress can be a suitable choice if you are in good alignment in all your sleeping positions. In other words a “less supportive” mattress can be a good choice if all the parts of your body sink in evenly and you are in good alignment in all your sleeping positions (see post #6 here). A mattress that is either too supportive or not supportive enough under different parts of the body relative to the other parts of your body is when you can have alignment issues.
It seems to me that you would likely do best with a mattress that has thinner or firmer comfort layers which puts you closer to the firmer support layers but it’s always best to have these types of conversations with a knowledgeable and experienced manufacturer on the phone because they will know more about the specifics of their mattresses and how they compare and which one would be the “next best choice” with the highest odds of success based on their experience and on the “averages” of their customers than anyone else.
Phoenix