I would say: Wizard 5/Daggerspell Mage 10/Unseen Seer 5\\Spellthief 1/Swashbuckler 3/Swordsage 1/Warblade 15
Take Daring Outlaw and Master Spellthief and for your Unseen Seer bonus spell: Hunter's Eye. You'd get 1d6 from Spellthief, +3d6 from Daggerspell, +2d6 from unseen seer, +2d6 from Daring Outlaw, and hunter's eye will give you another 6d6(?) for a total of 14d6. You have a decent BAB , so hitting with your TWF shouldn't be hard -- especially if you polymorph into something with a monster strength.
You lost one caster level, but you have a CL of 20 (Master Spellthief) and can steal spells to power yourself and you only lost 2 BAB.