I don't see how a snake goes from fuzzy mice to small rats or how a 2.5 years old snake just recently was switch to small rats from fuzzy mice????
Either the animal is very small for it's age or the age is wrong and you are not using the proper feeder terminology which does not help as to what to recommend for your snake.
Weigh your snake and weigh your feeders because everything is very confusing from your description.
Fuzzy mice are never fed to BP even out of the egg they take something bigger and small rats are 55 to 65 grams.