You are making a very wise decision, Saz! I quit caffeine over 20 years ago because of terrible symptoms no doctor could diagnose: rapid heartbeat, anxiety attacks, insomnia, can't even remember what else. It all seems so obvious now but 20 years ago not one of the at least 4 doctors I saw asked me about caffeine consumption. Cold-brew like you've been doing was not a thing back then but I drank black coffee from morning till night. It was only after reading a book on my own about the elimination diet that a lightbulb switched on and the first item I eliminated was caffeine.
Youre right that withdrawal is no joke but hang in there. As I recall it did not last more than 7-10 days and then it was completely gone and I felt 100% better. I haven't touched it since unless by the hand of a careless server who gives me regular instead of decaf in which case I find out pretty quickly and spend one sleepless night with heart palpitations, preceded by a brief period of euphoria which ifeels great at the time but I realize it's a harbinger for the ensuing jitters. I know that decaf has some % of caffeine depending on the brand, but I'm ok with it. You'll have to see how you do. Too much chocolate can also be an issue but for me a little is ok.
Best st of luck! After you get through this tough time, you'll feel so much better.