Starting formula after 5 weeks

So in my opinion FED is best and I don’t care for any negative comments. Soooo with that said.. My first baby I had always done formula and breast since day 1 but with my second, having her at home and knowing that I was able to breastfeed my first I didn’t even have any formula anyway so she’s been only breastfed since she was born. I got a job interview for a simple part time job and I have applied a few other places the only problem is that having a 2yr old 2 dogs and a home to take care of I’ve never made the time to pump and build a storage so if I start working I’ll have to supplement her with formula while I’m away :/ idk how to start her on it or what kind will be the most gentle on her stomach given that she’s only ever had breast. ALSO I’ve been thinking she has some kind of dietary sensitivity because of a bunch of reasons but I was already considering doing an elimination diet to figure I out. Any advice?