A large rat fuzzy or small rat pup is fine. Are you feeding live or F/T? If feeding live, I would stick with smaller prey. Smaller prey = less likely to hurt your snake.
I agree with the chart posted above by Bogertophis for size of prey, but not necessarily frequency of feeding. Once on rat fuzzy's or pups, I would be feeding every 7 days, especially given how healthy your snake looks. No reason to rush growing him.
That's my two cents.