I would keep it simple.
Data you don't provide can't be taken or observed.
What I mean is, don't do everything on one device. You mentioned banking, do you really need this 24/7 in your pocket? Or can you use it stationary at home through a computer or tablet?
The latter would mean that your bank can't track you and when your phone gets stolen, nobody can access your bank account and history. (this is independent from GrapheneOS).
Do you travel large distance to unknown places or do you stay local in your city or village? If the latter, print out for yourself the local map on old fashioned paper and carry it with you/in your car. So you don't need to use any maps or location services to navigate.
Public transportation etc sadly often does not give out printed tickets anymore. If you want to avoid being tracked by that, buy a very simple android phone or use your old phone (after resetting it and deleting all personal data) for installing the transportation services app and only use it for that purpose and nothing else (you probably will need to connect to a public wifi or something to buy and upload your tickets, but if there's nothing else on the phone, no contacts, no pictures and so on, there's not much to find on it)
Basically, when you can do something without an app, then don't use an app for it!
Things you don't need 24/7 can probably be done stationary at home on a different device or on a device used only for that.
If you need to be accessible for phone calls 24/7, maybe buying a second simple phone (preferred a dumb phone for longer running time) just and only for receiving and making calls will be fine.
We people do too much on an universal device and wonder about privacy and security.
We should keep in mind that nobody forces us to do everything digital and on one single device.