Right now i'm thinking of evolving it at lv 26 when it learns giga drain. then teach it energy ball, shadow ball an u-turn. :/
If i was you, for Cottonee I'd train it to 37, if possible. For the move Cotton Guard.
But with Whimsicott,
- Energy Ball
-Shadow Ball would cool for it, I'd do it ha
-Cotton Guard/Light Screen For defense
-Anything you want, Maybe Hurricane at 46?
if there's an item that helps accuracy it'd be perfect for hurricane
Hope that helps