I haven’t done a leisurely migration in a long time. My last few batches were because the hosting companies went down in flames, and I had to move as quickly as possible. One I had to restore from an Amazon or Backblaze backup because the losing server became unresponsive in the middle of an SCP session.
So since I have the luxury of time with this one, I’d like to make it seamless. The program you Googled to isn’t what I had in mind, but it will work. I can cron it to run, say, once a day until the move, and then do a final run immediately before changing DNS.
Richard