Advice on switching to formula

I usually breastfeed but last week I had mastitis that turned into an abscess and had to have surgery. I know have a huge hole in my chest and connected to a wound vac. 😩 I’m pumping but can’t use my milk because of the antibiotics & pain pills. I have a huge frozen storage of milk which I’ve been trying to use but every bag seems to smell like metal and my little is fighting it! I want to just switch to formula for her! Do formula fed babies get fed the same amount as breast milk babies?! Will this sudden change have an affect on her tummy?! Is there anything that I should know before switching?! TIA 💜