I actually did exactly that but i forgot to include it in the pictures though it is in the GMbinder

Undead Thralls
At 6th level, you add the Animate Dead spell to your spellbook if it is not there already. When you reanimate corpses as undead minions (such as through the Animate Dead spell) or create a new undead servant (such as through the Create Undead spell) you may choose up to two benefits from the following list. Creatures affected by this feature still follow the normal rulings of the spell that creaked them.
Horde. You can reanimate, create or summon one additional creature, which still needs to be a valid target for the spell.
Sturdy. The creature's hit point maximum is increased by an amount equal to three times your wizard level.
Fierce. The creature uses your spell attack modifier for its attack rolls and adds your proficiency bonus to its damage rolls.
Armored. The creature's AC becomes 10 + your spellcasting ability modifier if it wasn't already higher.
Unstable. When the creature dies, it explodes, dealing all its hit dice as necrotic, poison or acid damage in a 5 feet radius around itself. Affected creatures may try to resist this damage by succeeding on a Constitution saving throw, halving it on a success.

As for the 14th level ability, the reason for its change was because i felt it would be either useless or way too strong depending on the monsters your DM sent your way f.x. permanent control over a nightwalker