Have you tried Open Street Maps? You can get their app from F-droid.
Edit: Maps (Offline OpenStreetMap maps) - https://f-droid.org/app/com.github.axet.maps
Edit: Maps (Offline OpenStreetMap maps) - https://f-droid.org/app/com.github.axet.maps
For the record OpenStreetMap doesn't have one official app. It doesn't even have any "official" apps. People use OSM data to make other maps.