Hi digitaldave11,
I don’t know the options they have available to make changes to your mattress but either one or even both of these would be options that would likely move you in the right direction yes. Changing the upper layers would have more of an effect on pressure relief and comfort which appears to be the issue you are facing although all the layers of a mattress will have some effect on all the other layers as well and any change to softer layers can make “some difference”. If the only issue is that your mattress is too firm then adding a topper would also be an option to add some additional softness and pressure relief to your mattress but of course I would work with fine tuning the mattress first whenever that’s an option that is available to you.
I can’t feel what you feel or see you on the mattress so there is no way for me to know this. I also don’t know anything about your circumstances or body type or how much time you spend in other sleeping positions besides your stomach (most stomach sleepers only spend a minority of time in their stomach) but even if I did there are too many unknowns, variables, and personal preferences involved for anyone to be able to predict which mattress or layering someone will do best with based on specs (either yours or a mattress) or “theory at a distance” (see mattress firmness/comfort levels in post #2 here). Your own careful and objective testing (hopefully using the testing guidelines in the tutorial post) will be a much more reliable way to answer this than any comments I could make . Having said that your layers are firmer than many (but not all) people would choose but this would also depend on your body type, weight distribution, and physiology and the other positions you sleep in besides your stomach.
Phoenix