LUXE by Lisa Vogel swimsuit c/o Swimspot, H&M collar necklace, Zinke romper c/o By Langley (also seen here).
This romper from ByLangley reminds me a bit of an old-timey swimsuit, so I think it would be cute worn over a modern suit (especially one with pretty lattice detailing!).
Also, don't judge my impracticality, but I have actually worn this necklace to the pool. I usually just wade/float around anyway so there isn't really any danger of it getting wet.