Squishy sorc problems

I'm a level 50 lightning sorc and feel extremely squishy to some sources of damage.

I've got 1.1k life, 300es, resistances are all at 70%, however, my armour, evasion and block are pretty much at zero.

How the hell do I build up damage mitigation like evasion and armour when my STR is at 13 and DEX at 35. Do I just not level INT?

I can see how better gear would give me more life and ES, but not armour or evasion since I'm INT based. Am I not understanding something?