I started with cloud backup, it's going reasonably. I'm using something called Jottacloud which so far has been solid for me and has a lot of different types of backups. Migrated some-odd 25000 photos, slowly getting through the rest of my stuff on google drive. Soon I'll be below the 15g and switch to free it'll be great then I can work on the rest of degoogling

It takes so much work and feels impossible the entire time especially while all the rest of life keeps happening. One step at a time I guess

It's very simple. Buy your domain for the next ten years for under $200. Then find an email provider where you can bring your own domain. Namecheap has always been good to me. Maybe also Hetzner in Germany?

Hetzner provides email with their cheapest webhosting package at €1.60 a month.
Namecheap is a little more pricey than I expected. You pay $89.28/2 years with a promo code - Renews for $143.76/2 years

As others say, buy a domain so it's easier in the future.

But one thing what helped me was relay email addresses. Whether that's Addy, Simplelogin (now owned by proton so probably not), Firefox Relay, or another. When you sign up to shit, buy something, etc, use one of these email addresses. When you eventually move to your new email address, you can cutover all those accounts to the new one by changing the settings for where it forwards email to.

You can also use your own domain with a catchall and make up your own whatever@yourdomain if you're ready for that.