About 2 months ago, I ordered 10 swimsuits off of Amazon in an attempt to find one that actually fit, and didn’t want to spend a ton of money of something in bra sizes. I’m a 34GG (34J US) and wear a size large for reference.

This one was the best by far. The ruching is super flattering, the halter distributes all of my boob weight in a way that doesn’t hurt my shoulders, and it’s very supportive because of the band at the waist.

This is the other one I kept. I had to adjust somewhat frequently when actually wearing it, as it’s far less supportive, but I didn’t spill out of it at all.

I bought this one a couple of years ago, but it also holds me in/up nicely. (I have it in a 12.)

Honorable mention goes to this one that I actually saw recommended in this group. (I bought both the one with the crossover straps and the one without.) I didn’t end up keeping it because it didn’t feel very secure, but I know it’s worked well for other people of a similar size, so that might just be a personal issue.