I use whatever the one flippy cover style case that was available when I bought my phone is. It provides a reasonable degree of minor scratch protection when it's rattling around in a bag, so I don't feel the need for a screen protector, and it doubles as a little stand which is very occasionally useful.
Sadly, while the case is magnetic, the phone (Moto G7) doesn't understand that it should wake up and go into standby in response to the cover opening and closing. With the Moto G4 I found this really useful, and while the proximity detection and fingerprint scanner takes care of waking it up, I do miss it locking the screen automatically in response to flipping shut.
Barakta is a big fan of this style case, as it means she can hold the phone securely in her left hand.