Simple Defense from Convekta, but wait for a deal on a package set.
http://chessok.com/shop/index.php?main_page=product_info&cPath=7_26_37&products_id=408
Subscribe to their newsletter for deals. Advanced Defense is the next up, also available in one of the packages but is quite tactical as many defensive resources need a creative and forcing solution.
Soltis' book New Art of Defence in Chess should be next on your list.
I need to learn how to defend myself. Any good book suggestion that is not too hard?