I bought 2 expensive maternity suits (UK brands) and neither of them were any good! The first was a tankini, which had really tight elastic around the waistband - I'd bought a size up and it was still too tight at 17 weeks, so I can't see how it would've lasted me long! The top half had support but was quite short, and the super-tight waistband came to precisely mid-bump, where an over- or under-bump would've been soooo much more comfortable. It was like it hadn't even been designed for pregnancy, let alone specifically FOR pregnancy!!
So I sent that one back (losing out on a load of shipping costs) and bought a one piece style with ruched sides so it'll accommodate my growing bump - it's fine bump-wise, but it's really low cut at the back which means the sides gape and I have half a boob hanging out each side, and that's not exactly the look I'm going for. I'm used to the lack of support issue (I'm a 38F even when I'm not pg) but lack of coverage??
For lack of support - if it really becomes a problem, you could do what I used to do in the days before cute swimwear with any support, and wear two bikini tops, one under another, in colors or patterns that go together. Nobody ever seemed to notice and it certainly made me feel more secure.
So although I've kept the half-boob exposing suit as it's comfortable once I'm in the pool and swimming, I went and bought a regular tankini as well. I got one designed for tall girls, and bought a size too big. It's got a great longer-length top that provides plenty of cover for my bump, and the shorts aren't too tight - I'm planning to replace the elastic with a drawstring when I get bigger/have time. It's 100 times more comfortable than any of the maternity swimwear I've found, and was far cheaper.
I just ordered 
Have these people never heard of underwire????
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It only comes in black, which wouldn't really be my first choice, but it will get the job done.
