Tankinis Loz, they're brilliant
Lots of shops (Debenhams, BHS for starters) sell the tops and bottoms separately too which makes it even better. Some tankini tops are quite a bit longer than others so you are quite covered, but somehow they look a lot less formal/fuddy-duddy than a one-piece. Or maybe that's just me
I have some nice high-leg but also highish-tum bottoms which look nicer with my new one that the pair that came with it.
And a pair of short-shorts bottoms in bright turquoise which go with the new one and the slightly tatty old bluey striped one