Two reasonably good books you might want to check out are these:
http://www.amazon.com/U-boats-Kaiser...1596400&sr=8-1
That one has a pretty good Type UB111 cutaway drawing some waterline profile paintings of most of the WW1 U-Boats. Also check out:
http://www.amazon.com/U-Boat-Crews-1...1596400&sr=8-3
This one has good info on uniforms, medals, badges etc, although it does concentrate more on WW2 than WW1, which is hardly surprising since there tends to be more WW2 info around.
Both books do contain one or two minor errors (mostly typos probably), but generally speaking they are pretty good books and an interesting read. In any case, you can spot most of the (very few) errors in them anyway, as there will be contradictory info in one or two places which by a process of elimination enables you to suss out the real info.