Well, you are dealing with a vowel digraph < oo >. All vowel digraphs have multiple phonetic realizations. These realizations are not random, but are related. You also need to work out pre-r and pre-l environments separately.
/u:/ - food, boot, cool, google, moon
/ʊ/ - look, good, wool, foot
@5jj. It's interesting to me that you include "cool" in that group. I think that's what might be considered a Queensland pronunciation here, also school, pool etc. I hear my cool and most of the cools around me in Melbourne as being closer to a slightly longer "wool" sound, likewise in NZ.