Thanks for very kind comments. I returned the Office bag and got the Back Roller.
I change the shoulder strap hooks as suggested, but still it was not comfortable enough.
I feel like Arkel Bug or Commuter would be a better choice, but my wife didn't like the price. (two panniers vs 1 .. lol. that's what she says)
Anyway, Back Roller at least work for me, so I'll keep it.