Would they take a bottle of expressed so you can see how much they're getting?
Agree with both comments ... I express a bottle a day during the night when the milk hormone is highest to give her the next night before bed and always use nappies as a guide to being confident with feeding. I also get her weighed regularly (unnecessary to do it super regularly) to just check on weight again because it encourages me to keep breastfeeding knowing it's all going okay. Family hubs do weigh in clinics throughout the week that are free, that may give you some peace of mind or make you consider combi feeding potentially x
Signs he’s getting enough are he’s generally content, plenty of wet nappies, and continuing on his growth curve. If your little one hasn’t had a bottle before I don’t think this will help you to know how much they are taking, as they will probably take less from a bottle anyway. He may have had a growth spurt in length and just look slimmer, but if you have any concerns at all I would give your health visitor a call.
Baby should he gaining weight and feeling content after feeding, unlatching at the boob can be for several reasons but I’d definitely contact your health visitor and tell them your concerns. I’d also try weigh him so you can tell if he is loosing weight. I take my boy to the Library to get him weighed every month x