New Mom Feeding Question...

Okay so my baby is 12 days old and I started by nursing. But I hate not being able to determine if he’s eating the amount he should be.. I’ve tried pumping and feeding him by bottle but I can’t keep up with his eating.. I’m thinking about switching to formula feeding but I wasn’t sure how to go about it.. so my question is do I need to call his pediatrician and ask her what formula to get? Or can I get some formula to try and just let her know I’ve switched at his next appointment?

Please do not preach to me about how I should hang in there with breastfeeding or how it’s better for him. I do understand that and I want what’s best for my baby boy BUT my mental health is going down hill with nursing and me being healthy is healthy for him. I’m a firm believer in FED IS BEST. So please be respectful and keep those kind of comments to yourself.. thank you all💙