I hate to tell you this but the person that adviced you to feed your BP pink mice is an idiot. Just because someone works at a petshop or owns a petshop does not mean that they know anything about the animals that they sell and sadly it is like this in almost every pet industry. Depending on the size and age of your snake I would start it off on rat pinks if it is small but if it is a little larger I would just feed it rat pups. A 120-140 gram snake can very easily eat rat pups without a problem. Ball pythons should never be fed pink mice.
HTH