The flash over to GraphineOS was super easy! Downside is no call filtering/holding features, NFC payment, banking apps and some notification issues with apps that only supply notifications using google push services.

I'm quite happy with it, better battery life and you truly have full control. Nothing is 100% and even if you want you can download Aurora Store thru F-Droid to download apps from Google Play Store with-out even needing an account. I wouldn't be surprised if I flash my primary/work phone to GraphineOS.

But there is plenty out there to make your own custom OS too, based off Android. It's a lot of work to cut out all the Google parts though.