Hello Molly Kent,
Yes, there are many options for boys. I believe starting from the beginning in a body suit will add confidence. Just like anything else, we start from the beginning and progress slowly at our own rate. The fact that your son is wiling to continue swim class as the only boy says a lot already. The confidence will come in due time. Here are two options to get you started:
Please tell your son for me, a former shy swim team girl, “Do what you like and be true to yourself.”
Personal Trainer~NAPS 2 B Fit…
I suggest a shorty wet suit or board shorts (surf shorts). And a UV rash guard would go with the surf shorts. It is a very popular combo here in Hawaii and on the US coasts. I would also recommend having someone in his out of the family circle tell him in a sort of off the cuff way that everyone has insecurities. I used to tell all of my team kids that if you act like you are confident, most other people think you are confident. And just for my two cents, a foreign language, music lessons to learn at least one instrument, and having a fitness instructor are things that will make his life better, guarranteed.