Hi TnTWalter,
The first thing I would suggest is to try and narrow down whether your mattress is too firm or too soft in either the comfort or support layers. For this it would be helpful to know which combinations you have tried and what the specific differences were between them in terms of the symptoms you experienced and the specifics of how they changed with each combination (which symptoms became better or worse with each one)
I would also be aware that PPP (Posture and alignment, Pressure relief, and Personal preferences) can be very individual and your layers wouldn’t feel as firm for many people as jkozlow3 has suggested and it’s certainly not “out of the range” of what many people would sleep on. There are many forum members who have chosen firmer mattresses than you are sleeping on either in a 9" or 12" version.
Lower back pain can happen for many different reasons but it’s more common that it’s a symptom of a mattress that is too soft than one that is too firm. There is more about some of the more common symptoms and some of the possible causes behind them in post #2 here and the posts it links to that may be helpful with some of the detective work that may be necessary.
It may be worth trying to take a longer nap (or several) with your soft layer folded in half on one side and removing your firm layer underneath it. This would give you a Firm/Medium/Soft/Soft configuration and I would leave the cover unzipped which would give you a combination that would be significantly softer than what you are sleeping on now so you can see what the difference would be with a softer mattress. This would provide a very useful pointer.
If your husband is willing to go along with it for a few nights I would also try your soft layer as the second layer down and then use a medium on top of it. This would mean that you have a Firm/Firm/Soft/Medium configuration which would give you a little firmer sleeping surface. You could also go firmer yet and try Firm/Firm/Medium/Medium if you have these layers available to try.
These combinations and your experience on each of them should act as a useful reference point to see which direction you may need to go.
Phoenix