And book cases are too sturdy.. Not fun to hold in hand.
So i recommend making a DIY hybrid of the original honor 10 case and an adjusted Flip Case.
This has the added advantage of offering extra protection for the screen/front camera as well, even if you already use a tempered glass.
-Order cheap flip case from Aliexpress
-Cut out the hard plastic case and throw away
-Turn around flip cover and cut a new hole in it for the back camera
-Cut off the flip cover 8mm beneath camera, and throw away
-use quickglue to glue the original Honor transparent case in it.
-Reinforce the cut camera hole with glue.
You may want to cut out the magnet as well as this might interfere with compass or other functions in the phone.