Hi Hannah, I had trouble getting my 2 week old to latch to one boob. I saw a lactation nurse and she gave me some great tips. Happy for you to message me if you’d like? I can try and talk you through some of the things I did that worked
He might be confused if he's used to the bottle. They have supplemental nursing systems that can be used to get a baby back onto the breast (basically supplements their feed while they learn to suck at the breast effectively so they don't get frusterated and give up on the feeding before getting any milk from the breast). If you have access to lactation consultants or even le leche league near you it may be worth asking about. One of my friends successfully used it to get her little guy to breast feed after she had to start him off with bottles when her milk was slow to come in!
My LO had a tongue tie too. We were in the same situation as you, jaundice, mixed feeding both expressed breastmilk and formula (we used a cup and bottles). After he got his tongue tie snipped, he still didn't know how to latch. When he was around 2 weeks old, I reached out to my local breastfeeding support group running by a health visitor. The group was super useful, they taught me how to do deep latch and shared a lot of tips. My baby is now 17 weeks and I'm exclusively breastfeeding. Maybe ask your health visitor or midwife about the support group? Hope there is one near you.