To make the forces more distinct, I'm just putting them on the space wolves.
Likewise, the Thousand Sons all get sidearms and always wear helmets. They're the cold and calculated side, the wolfs are the passionate and raw side. To that end I hope to get some nice space wolf heads from a friend to really make their side more fleshy.
I have been thinking along the same lines. However, my solution was Mark III armour for Space Wolves and Mark IV armour (from Calth) for the Thousand Sons. For me, it helps distinguish the armies whilst fitting the theme perfectly.