TomboyX is a well known brand specialising in gender affirming underwear. They sell a wide range of clothing including swimwear! It's high quality, with a higher price tag to match. These wouldn't replace a binder, but could be a great option for taking days off.
https://tomboyx.com/
Twitter: / robynholdaway
Tiktok: / robyn_holdaway
Insta: / robynholdaway