supplementing

My baby is almost 8 months and she's only had breastmilk (breastfed or bottle). Lately I noticed a big drop in my supply. I was pumping about 20 oz a day while at work and now sometimes only 12. She drinks around 16oz while at daycare so I'm afraid at some point I'm going to have to supplementing (right now I still have frozen milk I can keep giving her)  My question is: should I supplement with more solids or should I start adding formula? 😭 I really want to make it to 1 year but I don't want to stress so much if I'm not able to. She's eating solids fine so I'm not sure what to do.  

Thank you!! :)