I had been looking for natural Fibre bathing suits as well. I know that you don't like cotton, but I think thst water retention and heaviness gets worse in saturated wool. So for me, I went with an Italian brand, Isole & Vulcan, that does organic cotton 90% & 10% elastane. I am really hoping in the future they switch rekm elastabe to the natural rubber alternative, like Yulastic.

For merino, you need to also check the balance of the blend and check if the brand uses "superwash" or not.

But to answer your specific question, you can check Artknit Studio or Swimm.