I attended a boat jumble some time back where I came across a store selling cheap life jackets. I bought 3. They are of course CE approved etc etc and do work. "never tell your 6 yr old to hop into the sea for a wee when wearing an automatic". She has adopted a nervous twitch every time I've asked her to slip it on ever since.
Anyway, the company was called, strangely enough "cheap life jackets". I think I paid £30 for an automatic. Tel No - 01922 419214. I'm sure they also have a www.