Hi Rebecca, it is true that a wetsuit will give you some buoyancy. Buoyancy is the result of the tiny bubbles trapped in the neoprene which act as insulation. The side effect of these bubbles is improved buoyancy. A bigger, thicker wetsuit will have more neoprene (and more of these bubbles) making it more buoyant and vice versa. So a long thicker wetsuit will give you more buoyancy than a short thinner one.
But what is even more important – wearing a wetsuit is no replacement for a life jacket. The added buoyancy is not so big that it could replace a lifejacket or to keep you safe in rip currents.