Buying a bathing suit is stressful enough as it is, when you add the 'problem' of big boobs it can be even worse. I looked into it more a couple of months ago when a friend was off to Mexico with her husband. She hadn't worn a bikini in many years because of this issue and I assured her we would change that.
We found some great options, and I have even more here for you. Nothing beats trying on a ton of them, and don't forget that you are not the problem - it's the suits. Just keep trying until you find one you like. It's good to order from somewhere with free shipping and easy returns.
Let's start with this Soda underwire top from Figleaves-
It comes in black and a huge array of sizes from 30D to 40E.
They make one that cuts a bit lower in front (this comes in black too)-
They also make lovely one piece suits-
This Delano top is really pretty and comes in all sorts of cup sizes -
You can also check out suits according to your body shape -
At Nordstrom I like this Bikini -
Don't despair - you will find the right suit! I will do more posts on swimwear in the future, so feel free to write in questions.