30C here. The solution to this problem is padded bikini tops. Victoria's Secret has them. I prefer soft pads in triangle tops, not much but enough to lift and boost. It looks perfectly natural. Or you can go for more structured tops with more padding.

Try an underwire style.

I have average boobs 34Ds. However I'm broad and the appear far apart and I'm tall so they actually look pretty small on me. I've always worn the triangle halter top bikinis and they do nothing to enhance my chest. Those tops make me look flat.

Any suggestions for swim tops that lift and enhance my boobs?