Another Place, Another Time is a great one, about the author and the type IX. I was going to recommend it when saw your OP again a notice it.
U-boats of the Second World War: Their Longest Voyages is also quite good to understand and know more about the experiences and patrols of the type.
And the famous "The U-Boat: The Evolution and Technical History of German Submarines" has a lot of the type IX also, and all of the others...
