Thin Life Jacket?

I'm looking for a thin mens, medium-sized life jacket. Does anyone know where to get one or stores that sell life jackets? I've seen people wear them before and they look comfortable because they're so thin, they're kind of as thick as a sweatshirt or so. I believe they are wakeboard competition vests. But I guess they aren't coast guard approved? Why would they be wakeboard competition vests if they aren't coast guard approved? Does that mean that we probably shouldn't wakeboard with them on? I know how dangerous wakeboarding can be and we should probably wear coast guard approved jackets for it. If that's the case, we can use it for wakesurfing I suppose. Thanks everyone!