You could go Kensai and enhance your fists. The skill requirements are all easily attainable by Crusader. Power Surge is pretty sweet.

The problem, though, is you don't have maneuver progression.

The Argent Fist from Faiths of Eberron might have different flavor from your character's religion, but it's a Monk/Paladin multiclass, so it might work with your build. It allows the Monk AC bonus to work even while you're in heavy armor, if I'm not mistaken. Not awesome, and doesn't advance your maneuvers, but it could still work.