I have had one J.Crew bathing suit with an underwire and the cup size was too big for me. I am a 34B, if that helps at all.
I don’t know how big yours are, but sometimes strapless tops don’t work well for bigger boobs. You might have luck, though, because they have different cup sizes! Mine was a one-piece suit so the cups were kinda “one size fits all”posted about 1 year ago