1 year old constipation

So we started weening my 1 year old off of formula to regular cows milk and she is having bad constipation. Called the pediatrician and they said to give her a suppository and to not go backwards with the milk meaning give her formula again. My question is....what milk can I give her other than cows milk that would be good for her? Should I dilute the cows milk or just give her a different milk altogether. Any help would be appreciated