Try to find a 3-4 week old rat pup. They will weigh approx 60 grams. If you decide to do live, (which is often a great way to start a non eater into eating again) make sure to supervise the entire constricting and death of the rodent.

Before you decide to feed, it is best to get the husbandry of the snake set up before you get him, and make sure that he has Hands-Off time for 2 weeks. During this time, he will acclimate to his new surroundings, and it will give him a chance to settle in. The only handling, peeking, or any interaction should be for spot cleaning urine or urates (hard white chalky pee) or poop. Change his water once every few days, and monitor the temps and humidity, misting if needed.

After you know that his husbandry is all set temp and humidity wise
Hot spot temp: 88-90 degrees
Ambient air temp(or cool side): 80-83 degrees
Humidity: 60% or 70% for sheds

Make sure he has 2 identical hides on each side of the enclosure. The hides should touch him on all sides and make him feel snug inside. One on the cool end, and one on or near the hot spot. These can be fancy hides, or a simple flower pot water dish with a hole cut out. Even old tupperware will work.

You should have a thermometer/hygrometer to measure the temps. An accurite from walmart is 11$, it has a probe to go into the hot spot hide, the unit itself should be on the cool side, preferably in the middle of the tanks height. (Do NOT use tape inside any tank whatsoever) This same unit will also measure the ambient humidity as well.

After 2 weeks of no handling, you can offer the mouse or rat at night. Make sure to not disturb him on feeding day. You can prescent the room with soiled rat or mouse bedding on top of his cage, to get him in the mood.

I hope this helps, never hurts to ask