It's tricky to know what to do isn't it. For us the decision to top up was made when Ds was only putting on an average of 60 grams a week and his pead was concerned. He also has reflux so it was hard to know when he was hungry, but I do the same as you, offer a bf on both sides then if I have it ebm or formula. I can't keep up with him, he wants about 240ml some feeds and I have never been to good at producing milk. Unfortunately I have been sick and my supply dropped so now he seems more interested in having a bottle but I am still offering the boob and expressing so we can try to get him back to bfing.