I saw that this snake had supposedly had live meals prior to your ownership, but he's likely been refusing because of all that's new going on, along with you
needing to get the hang of feeding. Whenever he is big enough to take two mouse hoppers, try feeding the first one live, & have a second one f/t that is
thawed & ready for him to take IMMEDIATELY once he finishes the first (live) prey. Most snakes are pumped up & won't much care if the second one is live
or not...& with any luck, after a couple feedings this way, they often just accept the f/t by itself when offered at the next meal-time.
I'd avoid sizing up if you can...the more mature the mouse is, the more likely it will bite back effectively & harm your snake. And especially now, since your
snake has NOT been eating, he'll be a little off-guard.