6 weeks

Hi everyone!! My son is currently 6 weeks and me and my friend had our babies the same week. Her pediatrician told her to help him sleep better she can do a tsp of rice cereal in his milk and it may help him sleep longer... few questions: 
Is that ok to do? Or is he too young? 
Her baby is drinking formula, my son is drinking breast milk, does that make a difference on if the rice cereal is ok? 
I've also heard a bottle of formula before bed and then breast milk for the rest of the feedings may help him sleep better.. is that true? 
I'm a first time mom I'm just trying to figure everything out but I won't do anything unless knowing that it's safe.