[Timshel]

Start now with a forward from the old address. Might take multiple years before you are confortable deleting the old address.

[climb_stealth]

You may be right there. Will have a think about it. Maybe a filter to flag things and update as needed.

[RandomBacon]

I went from using Gmail for 10-15 years to catch-all using my own domain name with Fastmail. It took a couple of years to slowly make the switch, but it was worth it. I still monitor the Gmail just in case and it's not a big deal, especially since you can fetch it (and send from it) with Fastmail (I just keep a Gmail tab open to report spam).