Look at the Ultra series. I bought the Mategear Kyung Soo in XL, and there is plenty of rear coverage, comes high in back. I wear Medium in US suits, but XL or O in Asian suits, this helps a lot with rear coverage. The front pouch extends to cover nicely, no gaps, while it looks low-cut with narrow sides. It can easily stay on in ocean surf.
https://mategear.com/products/ultra-...nt=18569143302
I also bought a Mini bikini in XL but it was too low-cut to grip my hips to stay up nice and tight. I like that tiny Mini front look, and envy the guys who can fit everything into them.