I'd recommend both the Clay Blair books, "Hitler's U-Boat War: The Hunters" and "Hitler's U-Boat War: The Hunted". For more personal stories then "Iron Coffins" by Herbert Werner , "Hirschfeld: The Secret Diary of a U-Boat" by Wolfgang Hirschfeld and "U-Boat Killer" by Donald Macintyre. Also the Micheal Gannon books are well worth a read, both "Black May" and "Operation Drumbeat".
That should be enough to be getting on with for now