I know this is old, but here’s what I usually do.
Hanna’s Guide to Confidence in Swimwear
Step one: find a modest one piece online. Harder than it sounds, but there are literally no modest options in any of the stores around me, and they keep getting worse! My first go-to website for swimsuits is Lands End, because they have an mostly older clientele, so their swimsuits are more modest than those in stores. This year there were only a few good options, however, I liked all of them. They fit well, are pretty and flattering, and the material is thicker than usual, which I like a lot. They are also low cut on the leg.
Always check the sports swimsuits if you need to buy at stores. By definition they have to be more modest, because they are activewear.
Then, I find a rash guard. For me, it has to be a T-shirt sleeve... that’s just what I’ve always worn. I think the long sleeves would be uncomfortable and not as easy to move in. I’ve been stuck getting these online because, strangely, only the long-sleeve kind has been in stores lately.
Last but not least, I add a pair of board shorts. General stores like Walmart probably sell some of these. You can also find them in more expensive stores like Patagonia, and probably surf shops if you have those. Of course, there are a plethora of options online, but shorts are trickier to size than swimsuits imo, so I try to find them IRL.
That combination generally makes me the most covered person on the beach or at the pool. However, I’m totally fine and happy with that! It keeps me comfortable, and is very practical, as well as being totally modest. And the best part is, if for one reason or another (like chafing, which happens to me—sensitive skin) I need to remove the extras, that’s fine, since I have a good suit. All of that gives me confidence, so I don’t have to worry about it at all when doing various stunts off the diving board.