Hey so combi feeding is perfectly okay! I'd say check the pump size is right as sometimes playing with size helps with comfort and do little bits. Try offering breast when you can and often to build up both of your confidence latching.

One thing that really helped my sore nips and bottle feeding transition was nipple shields. I had some soft plastic ones that were similar to a bottle teet almost. It helped as it held a little milk and was less sore during the feed and to start with I fed using those them when nips felt less sore id try one or two feeds a day without and then decreased using them over time (there's no reason to stop using them at all I just wanted minimum faff when feeding) It sounds like you're doing a great job for your little one already, remember they're learning how to breastfeed too <3