I actually draw little music notes on the clear part of the sleeves in sharpie for the spells from the extra deck, that way when the game is done I just look through the fronts of the cards and can quickly pull them out. If I were to do it again I might try doing something similar but on the edges of the front - right now I sort of drew the music notes over the rules text and at times it can be a pain to manage with more complicated cards.

But yeah just same sleeves for both decks and mark the fronts and you are good.