Can anyone think of anything that isn't "dual-wield Manyfanged Daggers", because that's rather expensive.
Ha, beat me to it.
Well Fell Energy is of course a good bet other than that there really isn't anything to boost the Spell's bonuses directly. You can use a Metamagic loop to add on extra effects and improve them. Like Energy Substitution(fire) and "
A blistering spell deals an extra 2 points of fire damage per level of the spell. In addition to the spell's normal effect, any creature that fails its save against a blistering spell takes a -2 penalty on attack rolls and checks until the beginning of your next turn.". There are also a couple dozen ways to increase elemental damage in D&D using Metamagics too. Other than that, like any other TWFer just look into Sneak Attack.
However since it triggers off Fighting Defensibly (FD) you can hook into that. CW has a sword that increases the AC bonus when FD'ing and the MiC has two items, both use Swift Actions through, that do the same, if I'm not mistaken Dragon Mag has a named Bracers of Armor that also chips in there, and finally there is a Trait and a couple of Feats that helps out too. You can also pick up Combat Expertise and there is a bunch of stuff that hooks into that too so in short you really shouldn't have an AC problem once you can afford some choices.
Since the Spell Resistance scales off your CL boosting that would help out too; Consumptive Field ftw.
Edit - Oh and don't forget the Arcane Duelist. Dexterous Attack is +Attack/-Damage, combined with Expertise you'll have a +AC/-Damage which is generally pretty easy to offset, specially when you'll gian more AC than you lose damage and you can pick up a bunch of Sneak Attack.