Usually with moose your feet are going to be in water at some point. If you are river hunting then hips are pretty much standard. A minimum for me would be 18" LaCrosse Burly rubber boots. That said, in my area September can be fairly warm and a good pair of high hiking boots with insulate would do as the moose are still pretty high up.
If you are hunting with an outfitter I would ask him. The terrain up here varies a lot. It would help a little to know if this is a float trip, spot and stalk, or what.