I helped my partner with this and we ended up with a top called a “tankini” which is a bikini top with a light shawl fabric “tank top” that hangs down over your midriff and a “swim skirt” which is essentially a skirt with a bikini bottom sewn in. Usually she just uses that but we also got a swim gaff she uses if we’re gonna do anything but gently swim and float.

She says she feels confident walking around & when her bottom is under the water with it on you’d never be able to see anything. Also, imho it creates a nice look with the top being a bit flow-y blending with the skirt’s pleats. :)

Full disclosure I’m cis and masc so I’m no expert, that’s just what worked for her ymmv!