Since I am pre-op finding nice swimsuits is always a bit of hassle.
I did result primarily to skirted bottoms and tankini's. Usually, swimsuits without pre-formed cups are flexible, so they somewhat well adjust to small cup sizes.
My thought was that I want to cover my bottom with lots of fabric to distract. I also realized very quickly after starting HRT that I do not want to go into the pool without some kind of top. (well, at least in a public one, there is always the one in my backyard) I did start out with rash guards and then went to tankini's and I have a one piece suit with a skirted bottom...