I am new here, but wanted to comment about your question. The best, most supportive bathing suit I have ever had was purchased at .......drumroll please..... Wal Mart!!
What was important about it is the fact that it is a one-piece design with a halter top. The tying of the top at the back of the neck lifts and supports my chest (fiance said, "Your boobs look awesome!"

). Anywho, I am a 42D, so this is saying a lot!! It also has a "dress" skirt over the lower half to hide my belly and upper thighs.
The key is....
think halter top.
Hope this helps.