Getting the size right
Buy your bra size. A swimsuit ranged in FF has been cut for that cup depth rather than graded from a neighbouring size, which is what stops the bust sitting low or spilling at the top edge once the fabric is wet.
Brands
Panache Swim and Fantasie Swim both range FF properly. For a two-piece, see all FF cup swimwear, or browse every one-piece swimsuit we stock.