I bought this costume as a replacement for my old speedo one that had gone see through from years of use.
I am a size 10/12 and going by their details I think I needed a size 34 (assuming it goes by bust size and not EU size.. which is not clear at all!!), unfortunately I had to return it as maybe I ordered the wrong size but it was too short in the body, so much so it made my shoulder hurt. I'm not exactly tall, only 5'3" so I can't see that having been the problem. It was also made of a semi see through material, which was different from my old costume. I am unsure if this would have been a problem in the water but it was rather thin and I would have been self concious.