How about spell compundium?
If you cant get trapfinding, you need some way of getting summons/livestock/commoners to "test the waters". And you'll be doing it a lot, so I hope its cheap.
To be honest, playing smart and cautious has much more to do with winning ToH than damage numbers and skill checks. Spend your WBL on smart alchemical/wonderous items and you will be happier than if you try to optomize a bard.