sardello I share your frustration. You are looking for training wheels. I have been gradually trying to get away from google myself, unfortunately my work is on GSuite (so everything). What I did was start by getting onto the proton platform. I use protonmail to aggregate all my emails now. I did the same with proton calendar. That way at least I have access to all my emails when Im away from my computer. I really like protonpass and protondrive as well. You can't "send from" or use a gmail alias from Proton mail, but you can forward everything to your proton email at least. I am grooming contacts not to expect me to respond by email all the time.
Installing sandboxed google apps is a good interim step. They at least have limited access in GrapheneOS, unlike when you are using an android and they have access to everything.
Do you know about the Aurora store app? You can download most google play apps there anonymously.
There are still some apps that google just does better like google maps. I'm trying to get used to organic maps. I was thinking about just getting a good SatNav for my car.
Hope this helps.