i cast transmute often enough and detect life, seems to raise my alteration pretty quick. I also have never played a mage decked out in heavy armor... just seems un-natural. You wouldn't put a spell caster front and center in the middle of a fight, I mean, that's what companions are for.
On that note, Lydia VERY rarely gets killed, because mobs leave her alone when she kneels down. Except when I hit her with word of death... I load her up with healing potions (from practicing my alchemy) and hit her with a healing spell. Seems to work just fine for me on legendary.