I was in the same boat until recently. Got a Proton account. There’s trivial import setup that both grabs all your email from Gmail, and it sets up forwarding.

Then you gotta start changing your email in different services to the new one. Should probably register domain for your new email so that you don’t have to do this exercise again if you switch out of Proton.

Install Proton’s mail bridge and Thunderbird to backup all your mail. Has better search too.