Sounds like I have (well had, before getting UTD again) a pretty similar bod to you. Before having DS I wore bikini's. But after having him, and especially given that we were going to be doing swimming lessons, I personally didn't feel comfortable wearing a bikini. I spent a day (a depressing one) trying on all different sorts of bathers from tankini's, to one pieces before settling on a one piece halter. For me it is relatively flattering to my shape, hides most of the squishy bits, but doesn't do much for my short, stubby legs (mind you not much does). It was pricey, but well worth it because I've gotten quite a bit of wear out of it. Only thing I found a PITA is that because my boobs are quite big, when we would do swimming lessons they would kind of float out of place a bit. They never popped out fully, but the halter didn't do the best job of maintaining my modesty either. And, when you're holding a bub and are standing in chest deep water for the most of the lesson, keeping them and in place can be a bit of a challenge. So if I was buying a new pair for swimming lessons, I would be looking for something that kept the girls right where I wanted them and didn't provide any opportunity for escape

Personally, I think the best thing you can do is go shopping by yourself and try on as many different styles as you can until you find something that you feel comfortable in.