I was switching F around 5mo also but was extensively pumping till around 6mo. We did it in phases one bottle per couple of days (4-7). He never had any problems, he liked formula, I didn't have to mix BM and formula in a one bottle to encourage him to drink it. He go his first bottle at around 3wo but only with BM. From then he was having a bottle with expressed milk occasionally during day and from 3mo for every DF.
If you have any specific question, please ask!