I attempted this. I'm sure it's not water tight but it was successful at preventing me from giving away my usage data too easily.

In brief:

- a custom android ROM and NO gapps - no Google play services - f droid for apps - yalp store (from f droid) for must have play store apps (although support is questionable) - I took a new email from proton mail - OSM for maps. SUCKS but a good alternative. Can't complain. - dickduckgo privacy browser - then just avoid the big tech companies (google, Facebook, Amazon, etc)

Cons: a much less streamlined experience.

Pros: some peace of mind about data. Because the phone is more basic, you don't want to fiddle with it as much. Enjoy life!