I was exactly the same. I just introduced a bottle and then expressed when I could feel my boobs getting to full and then eventually it reduced my supply
It shouldn’t be painful - if you’re sure the latch is good has baby been checked for tongue tie?
I’d just start introducing an Oz at a time a couple times a day and go from there xx breast feeding apparently gets easier and the first couple weeks, I’m exclusively pumping and hate it. My partner tried to mix breast milk and formula a couple times rather than feeding separately and it didn’t work baby was sick every time so I’d defo avoid that xx