We have had great success in increasing our ball pythons wieght by a little more agressive feeding schedule. Our 07 bumblebee which we got about a month and a half ago came in at 276 grams. She is now up to 449 grams. We feed every 4 days. She could go up to rats, but has been scarfing 2 mice per feeding. We have had better luck with others and worse with others, but it seems to work well enough! If they don't take it wait a couple days and try again.

I would say yours sound on the light side and need more or larger prey.