Hi, I do it. I bf first for each feed and then top up with formula. I bf at night too, it keeps your supply up if you do it between 1 and 5 am. I did try formula at night thinking lo would sleep longer but she didn't! I pump at least 2 x per day too and take fenugreek, you do have to protect your supply or it will go. It works really well for us although lo has decided now that she would rather be bf than formula so I have to bf more during the day and then she has a bottle before bed and one in the day if I can get her to take it xx