Definitely do a mage. I'd suggest that you make a complete break with your past characters by making a character who will not use any armor or weapons, otherwise there will be a temptation to slip back into your habitual ways of doing things.
Assuming you work with Destruction magic, you'll need at least two ranged spells, since some enemies have immunities. These will take the place of your marksman. You'll also need a couple of "on touch" spells, which will take the place of a melee weapon. One powerful (and often overlooked) offensive spell is Absorb Health (Restoration) which heals you while killing your enemy.
Illusion is also a very powerful magic school. You can cast a Command on one of a group of enemies, followed by Invisibility, and watch from the shadows while the enemies destroy each other.

Spells, potions, and enchantments provide your shielding. Elemental shield effects are very powerful and effective.