I had posted earlier in the summer about a bathing suit from Newport News, that has an inner shape-control lining.  It took me a while to find the right fit, but the ShapeFX skirted bottom really works for me.  I wear a 14 dress with 38AB boobs, and originally tried a 12, and the bottom was gigantic.  I wound up with the build-your-own separates, in a 12 top and 8 bottom.  The inner lining is snug enough to hold a tuck, and the skirted bottom would hide any slippage.