I have a fabulous one piece that is actually a two piece with a crochet overlay that makes it technically a one piece.
And, I think everyone should wear what makes them happy, regardless of age or occasion. Of course, our surroundings do interplay with how we feel and whether we feel good in our outfit, but hopefully you are choosing a one piece because you really prefer it, and not because you worry about others judging you poorly! I'm a firm believer in making it OK by being OK with it yourself first.
Something like this:
https://shop.nordstrom.com/s/r.....it/4870886