First thing to do is install F-Droid which is an open source alternative to Google Play that only contains FOSS (Free and Open Source Software) apps. This way you can easily update the apps and find new ones...
All the Android apps are available on F-Droid unless otherwise stated.
One common feature among the following apps is being privacy-friendly.
This list isn't in anyway exhaustive so feel free to ask for other apps.
If you don't like F-Droid's design then you can use an alternative client like Aurora Droid. Aurora Droid also comes with a lot of repositories that you can easily enable.
Repositories: F-Droid is very strict about the apps that are included in the official repository but there are other repositories you can add to have access to more apps. Izzy's repo is a popular one which you can easily add.
Isolate the nasty apps that you can't get rid of (e.g. WhatsApp) and control the data they have access to. The app uses an Android feature called Work Profiles.
I'd recommend Organic Maps before OsmAnd+ nowadays. I've found it performs better and is easier to navigate. Power users may want to stick with OsmAnd+.
From their site:
Organic Maps: Offline Hike, Bike, Trails and Navigation
Organic Maps is a free Android & iOS offline maps app for travelers, tourists, hikers, and cyclists based on top of crowd-sourced OpenStreetMap data. It is a privacy-focused, open-source fork of Maps.me app (previously known as MapsWithMe), maintained by the same people who created MapsWithMe in 2011.
Organic Maps is one of a few applications nowadays that supports 100% of features without an active Internet connection. Install Organic Maps, download maps, throw away your SIM card (by the way, your operator constantly tracks you), and go for a weeklong trip on a single battery charge without any byte sent to the network.