Can you name the exercises you were shown, or link to a video or article explaining them?
I don't know if this could be a case of "what's good for me might be bad for you" but bad posture must be pretty common in today's world.
Did your back pain get as bad as OP's?
I've been playing some games in a retroid pocket 5.
Mind you, it doesn't run all games, nor all well, but could be worth checking out.