I am doing it right now and it's going well.
My steps are:
1) Sign up for free Protonmail (comes with free receive-only @pm.me address).
2) Forward all Gmail to @pm.me.
3) Use @pm.me address for all new accounts / signups online.
4) Create a filter (you only get one) in Protonmail that all mail NOT to or from <me>@protonmail.com goes to a new folder called "Automated" (this will catch both forwarded Gmail mail and junk mail from websites / companies).
5) Begin giving @protonmail.com address to personal contacts (never automated forms or companies).
6) Back up all Gmail mail records into easily indexable storage (either offline or cloud).
7) Send out mass email to all contacts to update my email address to @pm.me.
8) Close Gmail account.
I'm on step 5, and will be for a while (haven't figured out step 6 yet). It's working great - finally I figured out a way to keep my personal mail separate from automated mails.
