I did this some time ago, at about the same age (maybe a bit earlier) as you're doing having stopped bf at 4 days old owing to severe PND.
Relacation is proper hard going but can be done. Do you have a supplemental nursing system?? Fancy name for a bit of tubing taped to your boob to feed pumped/formula through?
What kind of pump? You need one of those industrial milking machine things or at the very least a battery powered one with good suction. I also hand expressed at every sodding opportunity even if it went to waste. Like, on car journeys when I was the passenger (obviously concealed, no one needed to see my boob at 70mph).
Good luck.
I also took industrial quantities of domperidone but I think it's been removed from market now... Fenugreek is a natural product but makes you smell like curry. I didn't mind but some might.
If it is all too much, then in the long run it really does not matter how you feed your baby as long as you're not spooning carnation concentrate into their mouth. My breastfed child (the relacation baby) is very fussy with food, prone to eat high fat and high sugar food, and was a bloody disaster sleep wise. My bottle fed one (much worse PND, relacation as likely as hell freezing over) is an omnivore, very lithe and slim, does not over eat, slept beautifully, etc.