Milk alternatives before one year?

My daughter is 10 1/2 months old and has been exclusively breastfed. I recently went back to work and I'm struggling to pump enough for daycare while I'm at work. Like.. literally no back up supply left and only getting about 6 oz pumped during the day.

Her pediatrician said to wait until one year to introduce milk (cow or anything else) but I really don't want to start her on formula and then have to take her off of it in a few weeks anyway.

Has anyone introduced milk prior to one year? What was your experience like?

I'm having serious anxiety about it!