What is organic baby milk?

Hi Moms so im breastfeeding but also wanna introduce my baby to formula you know just incase i run low on supply or she stay with a family member and i dont got enough breast milk what are y’all suggesting in how to introduce her to it she does okay some days drinking the formula but then there’s some days she’s not having it someone told me half breast milk and half formula i tried it and she didn’t like or is it just me lol btw im doing organic formula

My newborn daughter on similac organic gentle formula and we are on the wic program and her doctor gave her similac sensitive and she is throwing up cotton cheese and I'm really worried ? she takes to the similac organic no problem but today we started her on her new one today and on her dads side they have a milk allergy, what should I do, I'm calling her doctor and wic tomorrow I'm just worried about my baby girl my first daughter kind of had the same problem...