For a few weeks now, I am using dnsforge.de DNS-Resolver. Just a DNS with integrated block lists, nothing to install or configure. Works well for me, I only had problems once getting the login-page of a public WiFi. But one cannot configure the filter lists.
Used that one before, without root and VPN-based, but it stopped every now and then, had to restart it, was too annoying. I guess it was related to the issue with apps getting closed in background, not an issue of the app itself.
I will try this one I think! The UI is not really intuitive if you want to change anything 
But I guess I’ll manage to figure it out. Might have the same issues with getting killed sometimes on the Fairphone though, then I will go back to dnsforge.de