There are a load of off the peg wetsuits, just as there are drysuits. As a wetsuit works by letting some water in, the fit is not quite as important as perhaps with a drysuit, but does need to be a decent fit. As mentioned by others, the best way is to try them on. Maybe when you hand over your present voucher to him, would be to say "I've also arranged to go for a wetsuit fitting" then he can try them on in the comfort of a shop's changing room, and not on site whilst on holiday ?
