The best lycra skin I've used is the Blue Reef Royal Lycra. Well made, high grade material, excellent price, less than $50 on line, a little more at a dive shop. Henderson also makes nice skins, but they cost a little more. Anything made of neoprene , even 1mm, is a wetsuit, not a skin. Thin wetsuits are often called skins, but this is a misuse of the term.
I assume your son wants something that gives the feeling of wearing nothing ( the reason they are called skins), but which provides some protection from sun, stings, and minor scrapes. Lycra skins are ideal. Use neoprene only if warmth is an issue. It is not for me in 80F + water. 1mm or 1/2 mm neoprene jumpsuits are great for water in the upper 70's, but they do not have the effortless fit and feeling of skins.