Op, congratulations and well done - you are doing fantastically.
My ds is 11 days and we've had similar experiences with feeding. At night he's been feeding for four hour sessions, eventually fall asleep on the boob, we'd try to put him down but he'd scream until he was cuddled... and so the pattern continues! First community midwife said he just is a hungry baby (still not made up his birth weight), that it's 'completely normal' for him to want to be on me all the time and I'm ensuring my supply will meet his demands...
I've had the emergency formula staring at me from the bedside table and DH particularly wanted us to introduce one bottle in the nights so he could take some of the pressure off me. BUT I've been so worried about the 'teat confusion' the hospital midwives and the health visitor kept banging on about that I was too scared to un-do all the good work we'd done getting his latch right.
However, yesterday a different midwife came and said it won't harm to give one bottle of formula or expressed milk, that me sleeping is as important as exclusive breast-time. She also suggested lying on his mattress cover whilst feeding so it gets warm and has our smell then lie him in it to transfer him to his basket. She also explained how we could safely co-sleep and that it was safer to co-sleep than breast-feed sitting up and risking falling asleep that way (which I admit, I've done a couple of times and scared myself) I was really nervous and reluctant about co-sleeping but we did feel empowered after her visit because a professional had okayed it, and we felt we had some artillery against the night!
It did work last night; he slept next to me for five hours after his bottle of mixed expressed and formula. I was terrified when I woke to find what time it was and had to check he was breathing! Obviously, now we have the fear that it won't work again tonight but I felt more human this morning and like I can deal with tonight a bit better.
It sounds like you have had lots of positive developments and I in no way think that my way is the answer (or assume you've not tried these also) but I hope you know you're not alone in all this!
HCPs really should give more of a sense of the reality of bf. Perhaps they don't want to put people off but I know that if I'd been given a more realistic idea, even just about the length of time I could expect to be feeding for, that I would've been more emotionally prepared for it.