How much does your snake weigh and how much does the mouse weigh? It's easier for me to tell from two weights how big each is than descriptions which can vary from place to place.
My hatchlings get hoppers until they reach about 90g to 95g, then they are switched to adult mice. Even so, I've fed adult mice to hatchlings occassionally, and while it was on the large size and they needed an extra day to digest it, they did fine.