Have you considered expressing? With DD1 I went back to work when she was just 6 months old, 2 days per week.
I never considered formula, but managed to express her feeds. I was also lucky in that I ould drive up to childcare and breastfeed her at lunchtime. She started childcare in summer, and was refusing all bottles etc. Finally a few weeks after she started drinking EBM from a sipper cup (a Tupperware one) and we never looked back.
I would feed her on one side on waking (7am) while I was expressing off the other side. I would then express at work around 10am (on the toilet, no less
) then I would have milk for her to drink for the afternoon if required. I would then express sometime in the afternoon. I worked until 6pm, so then fed her a few times before bed. This worked well for us until she weaned at 15 months.