Congratulations on your new arrival! And well done for trying to find a feeding routine that works for you, through all the challenges.
If you can link in with your infant feeding team they should be able to guide you through the change. Or if you can afford a private lactation consultant, a good one is worth their weight in gold.
I'd imagine that you'd need to transition one feed at a time, to avoid any clogs / supply issues. I've heard moving too fast off pumping can lead to incomplete emptying of the breast so the slower you can move across within a reasonable timeframe the better I'd say.
For combi feeding, you'll need to stick to a routine on it. I would keep at least one breast feed at night time to keep your supply high, as prolactin levels are highest at night.
If you keep the bottles small in terms of Oz, it stops babies stomach getting stretched / them expecting more milk than you can give in one breastfeed. Plus use a slow flow teat, and paced feeding, to stop baby getting a bottle preference. If baby ever does refuse the breast in preference of a bottle, sometimes giving them an Oz or two of formula and then latching them on makes it easier - hunger can make them cranky little things!
Where combi feeding gets a bit challenging is during growth spurts. When babies cluster feed, especially around the 6 week mark, it can be discouraging. It often feels like they're not getting enough & it's tempting to just give more formula. The downside of this is it if you just give a bigger bottle during this time your milk supply doesn't get the signals to grow. It's totally normal for them to be on the boob non stop during a developmental leap or growth spurt.
Local breastfeeding groups can be a big help if you have any near you?
Best of luck with it! And remember, the most important thing for your baby is a happy, healthy mama so make sure you're a priority in your choices. ❤️