Today was much better. Still unsettled but he got a decent sleep this morning and had a grotty afternoon. He's working through huge poos, I assume that's because he's now pooing less often so they're bigger.
He's having huuuuuuuge feeds so he obviously hasn't been full properly before now, poor boy.
Onwards and upwards from here hopefully! Will definitely help him in the long term, his latch is already improving.