There are two things that I'd like to address. One is about one piece swimsuits for long torsos. I've seen them in Sears and the Bay (not sure if you have those stores), and in the Sears catalogue. I know that
Christina as well as other manufacturers make the Long swimsuits.
I also wear completely different sizes on the top and bottom, so I cannot buy single size bikinis. I wear a size 6 on the bottom and a D cup on top (nope, no doctor gave me that "problem"). Normally I wear a C, but the tops are so skimpy, I have to go with a D. However, there's a store around here called Bikini Bay that sells the tops and bottoms separately, so you can choose the style and size that you want. They also have certain styles that come as a set called 8D and so on, and they're whichever size bottom (like 8, 10, etc.) with a D top. The
Sears catalogue also sells tops and bottoms separately.
Not sure if those work for your areas, but there must be a solution. Oh yeah, when I've really liked a set, and the bottom's too big, my seamstress has taken in the sides of the bottoms for $5. You'd never know the difference.
Good luck!