Starting from lvl 13, you should be able to wear:
+ 6 Dex and Wis item: both could help to raise your AC
+ 5 Protection item (you are currently wearing +4)
+ 6 Armor item (better than mage armor; +8 AC bracers available at higher levels)
weapons of Parrying and Greater Parrying: +1/2 Insight bonus to AC (some items or combination of items can give you +3/4/5 Insight bonus to AC at higher levels)
Other items, a bit harder to find, could improve your AC:
Icy Raiment (
http://i153.photobucket.com/albums/s...IcyRaiment.jpg) (ML 14)
Chattering Ring (
http://i153.photobucket.com/albums/s...teringRing.jpg)
You didn't post your features; Combat Expertise (+5 to AC), Dodge (+1 Dodge bonus to AC) and Mobility (+4 AC, when tumbling) are defensive features.
However, other party members will help your AC:
Clerics can give you +2 luck bonus to AC casting Recitation
Rangers can give you +5 Natural Armor bonus to AC (better than standard potions)
Lvl 15 bards can sing Inspire Heroics, giving you +4 Dodge bonus to AC
Paladins will help your AC and saves with their aura