Bikini top for big ed! HELPPPP!!!?

Hi! I wanna buy myself a two-piece but I always have the concern about my . I like billabong's design, a lot, but most of them are triangular designs with spaghetty straps and I think those are easily fall off and only fit for smaller girls. All the other brands are either too y-lady-looking or granny-looking. I think I would like BANDEAU because they're sorta sewn to the middle and cover up my but I don't know if they'll "stay put" if I do sandboarding or other active stuff. Any suggestions? I live in Sydney, so I suppose this is a heaven for bikinis, I just haven't found it yet.