For our pup, we bought the Large Wired crate from a pet supply store.
It fits a 70 pound dog, ( even has a pic of a boxer for that size category) it came with an inside "puppy" gate to block off. I think this is the best as the wired crates have great air circulation and we have ours covered with a blanket and when he is in at night we cover the whole thing so it is nice and dark with a couple of squishy's and his blanets to lay on.
If you dont have a crate with an inside adjustable gate, then you can use a paper box to block off the extra area, so he will not do his business where he sleeps.
Good luck and i hope this helps.