Formula milk

Hi, need your advice mummies. My baby is 3 months 4 days. I’m going to work in few days after maternity leave. I have stored EBM in freezer but it won’t be enough. Tot of mixing formula milk From now so that my baby can adopt so one day when I stop BF she will use to it. Therefore I gave her Frisolac after few hours she vomited and she had rashes on her face. Next day I have frisolac , I’m only giving 2 oz per day. Other than that only BM. She had rashes also. I stopped for 1 day and she gets better. I consult dr and he say maybe can try other formula milk. He seems not giving much information. I did ask so can I give soya milk or goat milk or still continue cow based formula milk. He say up to individuals preference. Can give a try and see what suits her. Now, do I feed her more frisolac and see? I worry if it worsen her situation as myself and hubby has allergy issue. Shall I try other formula milk. I heard tt frisolac and Dutch Lady has less dha and better it seems... true? I have no idea how to choose formula milk. Shall I go for lactose free milk? Besides, doubt. After thawed frozen EBM, feed the baby and if she didnt finish it.. can offer again? Please help me.. Advice me regards to formula milk and EBM feeding.. thank you so much all Mummies out there. ??