PC, I've experienced the thrashing and the not sleeping and no routine and other things you've mentioned, and have never had a huge letdown or been able to express much.
However.... I have 2 dd's (2.5 years and 8 months) who are thriving.
What I mean is, the things you describe might not be a supply problem, and might not have any specific cause.
They might drive you crazy but not ultimately be a problem for your ds.
It's so so hard seeing them being unsettled and you feel there must be a cause and must be something you can do..... but we tried everything and in the end the only thing that made a difference was time.
OK, we didn't try absolutely everything... didn't want to ff so that was just not an option. dd1 had some ff topups early on under duress but nothing after that. So I can't comment on ff as a "cure" - but it sounds as if you, like me, aren't keen to go down that road anyway.
Erggghhh, I realise I've said nothing except "It will get better" which I imagine is pretty useless for you.
I'll echo others in suggesting a bf counsellor - they can check all the bf things for you so you can cross that off the list as it were.
Sorry, rambly unhelpful post - just wanted to let you know you're not alone in this!