Have you considered seeking consult with another PS? Maybe there is better symmetry that can be achieved.
I had a lumpectomy which was not so bad, till I had a 2nd lumpectomy and left me quite lopsided. And I was already smaller on that side to begin with! I have had a lot of bra troubles too, really having an A cup and a B cup is a problem. I found that bras with a little stiffness or form to the cup, rather than just fabric, works best. It does not pucker, just sits kinda empty in the upper part of the left cup. It helps the lopsidedness look much less noticable.
When I wet through chemo, I bought a prosthetic that was really marketed as an enhancer, not a prosthetic. I got a pair cheaper than I could have gotten one. I think it was called "Nearly Me" or something, just desinged to give some lift. I never wore it, fearing it would fall out, so it has collected dust nicely in the closet.
You may want to try a shop that specializes in post-mastectomy products, they will likely have what you are looking for.