Ask your DM to allow for "Extra Spell" feats not from your list.
I've seen a hexblade 12/Abjurant Champion 5 (thus, CL 17) with Shield (+9 AC) and Shivering Touch (3d6 Dex damage, no save.)
Minor Shapechange (CA) for 17 temporary hp/round, Mirror Image & Battlecaster feat with mithral full...