@msolga,
I sit in a reasonably priced Staples office supply chair that is made comfortable - after being discovered as uncomfortable - by two pillows, one for the seat (one of those cheapo pillows for patio chairs) and a slim pillow for the back. That one keeps slipping to the floor.
I hunch, I lunch, I get up and sit down, but mostly I've learned to move my torso, which is what those balls and ergonometric things are about.
Music is good for this, but simple tweak movements sans sound are good too.
Soz, I've read that straight up posture is a no no, as in don't aim to hold that continuously - and probably posted about that here. Alas, no link.
Of course, slinking your head down your neck for hours isn't smart - an old habit of many of us - but moving the spine seems to be smart, including a kind of slump as part of the movement.