I'd recommend Paton's Decor...Wool/Acrylic blend, but you would never know it! It's like a 3 ply cotton candy...Not an easy knit, it's splitty, but YUM!
I bought it at a LYS to sub a Vogue pattern's yarn for a toque and gauntlets for my niece (who's not going to hand wash anything!) At gauge, the stitch definition and loft are perfect (that Mmmmmm effect.)
Chances are good that you could find it in colors your son would care to wear.
Good luck with your project!