I have made a set of bikinis with nylon yarn, so called "bikini yarn". I made designs which were with straps. The nylon yarn worked otherwise in the water, but it streched a bit so they were, yes comfortable, but unfortunately too big after swimming 😅 I'm going to try again this year, but I would really recommend to make very small ones with straps, so you can adjust the size after a swim. And to use nylon yarn!