As covered over here, you actually don't need to bring up the spell wheel to change what you've got assigned. Instead - even though it's a bit cumbersome to do - whilst blocking you can use the D-pad (or scroll wheel on a mouse) to cycle spells whilst remaining in combat. This allows you to forever switch over to Quen (the spell that lets you soak up one blow damage-free) before then hopping back across to Igni (the fire spell), Aard or Axii (Force-push and mind-control respectively) to mix it up. Basically, you always want to have Quen activated (you can tell because there'll be a little glow around Geralt) before using things like Igni to torch packs of wolves or keep groups of enemies more spread out - and you can use Aard to blast many high-level enemies off the edges off cliffs for easy wins.
