You're in a tough spot. From right now, until you're solidly in Tier7 gear, you will struggle with balancing new items against maintaining a minimum defense of 540. After Tier7 it gets much easier.
Two things will help you:
The Seal of the Pantheon which drops in Normal HoL off of Loken.
Enchant Chest: Greater Defense a relatively cheap enchant, provides 22 def rating to the chest. Also, don't feel bad about gemming for Def.