My advice - just rip the bandaid off and do it. I had anticipated taking a whole weekend to update the email address on all my accounts, but it was a lot less painful than I had anticipated. Changing over ~50 accounts took me about 3 hours all told. Most services allowed me to change my email even if it used email as the “username.”

Using a password manager made this much easier, as I could easily keep track of which accounts I needed to update and which ones I still needed to do. I switched over to Fastmail and haven’t looked back.