This is the biggest problem with the Paladin class. If you cast any spells you feel like you are wasting your slots.
You can stack a smite spell that involves an attack with an actual smite for even more spike damage... thunderous smite probably best for this AIR:
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Of course you're burning through 2 spell slots to do this and probably doing less damage than if you added smite to a crit, so it's most useful at higher level when you have plenty of slots.