Elemental Armor

The caster of this spell touches one willing creature giving the creature resistance of one of the following damage types; Fire,Cold,Lighting,Thunder,Acid, and poison.  When the creature wearing the elemental armor is hit with a melee attack the attacker takes 1D6 Damage of the type originally selected.

At higher levels: When you cast this sell at level using a spell slot 4th or higher the caster adds one additional elemental resistance from the list above, and adds an addition 1D6 of the damage type selected. For example if the caster casts this spell using a 8th level slot the willing creature becomes resistant to Fire,Cold,Lighting,Thunder, Acid and Poison damage and when hit with an attack deals 1D6 Fire,1D6 Cold, 1D6 Lighting, 1D6 Thunder, 1D6 Acid, 1D6 Poison damage

Casting this spell using a 9th level spell slot gives the creature resistance to all damage types excepted bludgeoning, piercing, and slashing, and changes the damage dice from a D6 to a D12 per damage type. Dealing a total of 10D12 of all damage excepted bludgeoning, piercing, and slashing.

Please share any additional tips for how you might go about creating and balancing the spell I'm going for here. such as help with balancing the up-casting