Unfortunately, you made the right decision. Alteration's defensive spells are a joke compared to armor, even if you take Stability and 3x Mage Armor. I'll be improving this when the Creation Kit is available, but for now there's not much point to an unarmed character.
Each to his own, I suppose.
I am lvl 48 mage at the moment and am enjoying being un-armored (playing on adept level) and find that 3x Mage Armor is plenty. It's not the max of 80% reduction, but seems to be plenty for now. I haven't put any level up points into stamina, so I can't carry much, as it is. I wouldn't want to carry a whole set of heavy armor right now. I make use of a variety of tactics: paralyze, stagger, conjure, shout, ward and bound sword for soul capture, I am having quite a variety of gameplay. I think it is fun. For my own taste, I would not choose to be a straight-up warrior. I think for my next play through I will be an assassin/stealth/illusion type character. I haven't spent one single perk on illusion on this play through.
My magicka pool wasn't big enough for the dual cast Dragonhide, so i decided to level up alteration to 100 (I was already at like 96 anyway, just from normal use) so i could get the half cost for master spells perk. I cast the single Dragonhide on myself and let some bandits hack at me while I just stood there.... that was pretty interesting. Is this what Armor wearers do with max Armor? Even with the half cost perk, my magicka pool still wasn't high enough for dual cast, so I enchanted some fortify magicka items, and got the pool over 700 which is what it took for me. Having 0 cost for destruction saves my bacon when I use up almost the whole pool to dual cast Dragonhide. I cast it on myself if I am about to go into a big battle with a boss, otherwise i use my other enchanted items that don't boost my magicka pool so high (favoring other enchants instead) and use Ebonyflesh instead, which is fine for most battles. The only time I have trouble is with other spell casters that are using an element I wasn't prepared for... at least I have trouble until I change out some gear to mach the threat. The creative gameplay as a mage is what keeps it interesting for me.