I waas hoping you could help. DS who is 6 needs a new body protector, and not having any tack shops remotely near us I'm having to order it online. I've done his measurements and according to the sizing guide he sits somewhere between an XS and S, should I be sizing slightly up, ie the S baring in mind he'll probably have a sweatshirt under his bp or should I go snug? The measurements are done in ballparks if that makes any sense?