Hi maskedrose,
I think you are wise to wait a few weeks or so to give your body time to adjust to a new sleeping surface, especially since you have a tendency to slouch which the mattress may be helping you “correct” which can cause some discomfort at first. If you are still having some discomfort or pain after the initial break in and adjustment period then a topper can be a good idea if you need a little extra softness, pressure relief, and contouring for your mattress. There are some topper guidelines in post #2 here and the posts it links to which may be helpful if you decide to go in that direction.
I know from your previous comments as well that you are aware of this but your pillow can also make a significant difference in both pressure relief and in alignment when you change to a firmer sleeping surface because the distance between your head or neck and the mattress will be different.
Thanks for your ongoing feedback 
Phoenix