As someone who's done a lot of swimming I used to wear the full or half body training swimsuits, they're unisex anyway. You could probably wear something under a regular swimsuit if you wanted to. I mean, you could probably wear a bra under one. Can't see why not. If it's the same color as the suit I doubt anyone would even notice. If you're planning on doing strenuous swimming though I don't think it's a good idea.
These days I don't bother with swimming in the public baths as it's too much of a pain to get to, I just use the sea. Since it's typically very cold I therefore do it in a 3/5 mm male cut wetsuit, depending on the time of year for thickness. Male cut wetsuit is generally more comfortable since it has more room at the shoulders, because mine are rather big... and a lot of female wetsuits really do seem to have very dinky shoulders. Which surprises me because you'd think they'd cater for female swimmers better who also have well-developed shoulders.
Anyhow marine wetsuits and rashguards crush everything down as much as possible, no need to worry about that for me. Plus the fact the most inquisitive creatures around are only the fish.
