Most of us switch to rats after the mouse hopper or small mouse stage. You don't want a 1500 gram ball stuck on mice because then you'll have to feed it multiple mice per feeding.

When you feed the fuzzies, is there a visible feed lump? Or does it look like it hasn't eaten at all? Feed the size that puts a small, but noticeable feed lump in the snake. One every 5 days. It will grow very well this way. Then just move up in feeder size as needed. If the fuzzies seem too small you can give 2 just to get rid of them. Then buy the next size.