Here is a good feeder chart.
My Hypo Grææis on small rats and she is comparable in size to your dude. Between fuzzy and pup until 300-400 grams. 400-800 I usually stick to weanlings and smalls.

Remember, make sure the prey is about the same size or a little bigger than the widest part on your BP's belly. You measured him at 1.25 diameter and that makes me think you'll need a small rat.

Good luck from us!