supplementing with formula?

Ha
Please help!
I have been exclusively breastfeeding my now 10 month old since day 1. I returned to work when she was 6weeks old and it has been one long and tough road. She's great at breastfeeding. I'm not that great at pumping. My body just doesn't respond! I've been able to keep up day by day, but I'm out of breastmilk for her for while I'm working! I used to get 2-3 bottles per day (4oz each bottle) I'm not even getting 1 bottle per day now. So I need to start supplementing, which breaks my heart! I'm so close to 1 year but I can't keep up. I have enough milk for tomorrow, then that's it. And it's only because I was sick Monday and called off work. 
I want to give her the best, but I have no knowledge about formula and it honestly scares me. It's so full of junk, I don't want her to develop stomach issues either. Please help me out. I need advice asap!