True Mage Armor

You touch a willing creature who isn't wearing armor, and a protective magical force surrounds it until the spell ends. The target's base AC becomes 13 + casters spell modifier. The spell ends if the target dons armor or if you dismiss the spell as an action.

At Higher Levels: Casting this spell at 5th level or higher gives the creature resistance to all damage but psychic. At 9th level choose a damage type whether physical or elemental, creature is immune to that damage type for the duration.