Hi Kefit,
It certainly sounds reasonable yes although of course only your own experience will be able to tell you whether a specific thickness and firmness will be a good “match” for both you and the mattress you are using it on. The choice between 1" and 2" would depend on whether you are looking for “a touch to a little” or “a little to a fair bit” of additional pressure relief. The choice of firmness will also depend on whether you would prefer a little firmer “surface feel” on your sleeping surface.
There is also some information in post #2 here that may be helpful because issues with pressure points in the shoulders can also be the result of a pillow that isn’t the right thickness or firmness or from the type of mattress protector that you are using so it may be worth some experimenting to see if either of these make any difference before adding a topper.
I would also make sure that you are rotating your mattress on a regular basis (see post #2 here) so that any softening will be more gradual and even across the sleeping surface.
Phoenix