OK, here's a sketch. I'm templating this on the 5e half-casters, using the 4e Swordmage as a guide. It's not complete but I think this outline should work.
You meld magic and swordplay together to become a bulwark of the party. You're also some weird purple spiky thing who dresses more for Better Dommes & Gardens than D&D, but ya know how this game can be.
Caster progression: 1/2
Armor proficiencies: Light, Medium. No shields.
Weapon proficiencies: Simple melee, swords of all kinds
Casting focus: Your sword
Weapon bond: (See Eldritch Knight)
ASI schedule: Same as a Paladin.
Aegis: recharges on a short rest
Level 1: If you are not using a shield, add 1/2 your INT bonus to AC, rounded up (maybe this should just be your INT bonus?). Gain 2 Wizard cantrips of your choice.
Level 2: Choose Two-Weapon, Great Weapon, Armored, or Duelist fighting style. Get your spell slots. You start with 3 wizard spells known.
You gain the Arcane Defense ability. When you take non-physical damage, as a reaction, you can expend a spell slot, reducing the damage by 2d8 with an L1 slot, and +1d8 for each slot above that.
Level 3: Choose your Discipline. A Discipline adds an Aegis option and hits you with some extra Spells Known, same progression as a Paladin Oath.
Level 5: Extra Attack
Level 6: You can substitute a wizard cantrip for one weapon attack.
Leve 10: You can substitute a a wizard spell for one weapon attack.
Level 11: After a long rest, choose one fire/cold/poison/acid/lightning. You do +1d8 damage with that element when you make a melee weapon attack.
==== Discipline of Whatever ====
Aegis of Assault (bonus action):
Choose an enemy. For the next minute, whenever that enemy attacks somebody other than you, you can teleport up to 30' as a reaction and make a melee weapon attack.
Aegis of Shielding (bonus action):
Choose an enemy. For the next minute, whenever that enemy hits somebody other than you, you can use your reaction to interpose a magical barrier of force, reducing the damage dealt by the attack by 1/2. This includes any poison or whatever, no loopholes.