Just remember three things when buying/using it
1. There should be no gap in between your helmet and your head...ever. Should be snug with no gaps. Nothing brain strangling, but snug.
2. Nothing more than a balaclava under the helmet...if you want full functioning safety of the helmet.
3. Rule number 1 applies to the strap. Shouldn't be loose at all. Should be snug, not killing you, but not enough to move the helmet around with minimal force.
As for what to buy.....whatever you like, fits, and it certified.
Im all for having fun, showing your tits and getting fucked up on a river float but it can be done without being a pig.