advice please!!!!

I wil be returning to work in 10days and in breast feeding... well for the past month if been trying to get my milk supply up so that i can continue breastfeeding while im at work ( pumping every 2 hours) but it does not help my baby drinks everything up soo.... i was thinking about substituting with formula for just 10 days while i pump and freez my breast milk (kind of getting a head start) is it going to be safe for her to drink formula for 10days and then pit her back on breast milk??? I need advice please