As far as I know the largest offenders are still the cellular companies since they can and are selling location data that works without any software on the phon

As far as I know the largest offenders are still the cellular companies since they can and are selling location data that works without any software on the phone. It's technically less precise than GPS/wifi location data but since it's always active it's pretty easy to use weeks of data to improve the resolution. Besides that just don't install any apps you don't need. Stick to open source software, install a custom ROM on your phone, don't use Google location services, etc.