I already had a bunch of cotton cheap sports bra and shelf bras - Hanes or fruit of the loom, so I brought those and just peeled off the wet one and put on a dry one when I got out of the tub.
I didn't want to buy anything special. This time if I can find a fitting bikini top I will use that or I'll just wear the cheapie bras again. I have a couple stretchy non cotton ones now that would work well too.
No bottoms. I kept it dark while laboring and the water hides things anyway.