I slump as well. I'm 21 years old and I spend most of my time sitting in front of a computer either slumped or with my feet up on the seat and my head resting on my kneecap or similarly poor posture. I'm curious what other people use chair-wise and if there's a fan favorite.
Try using a footrest, perhaps a rocking one so that your feet get to move a bit while working. It should help you maintain a better posture.
You should also try to get out of your chair and move about for a few minutes as often as possible throughout your day. Among other things, the slouching/hunching/shifting in your chair is often an attempt to alleviate the pressures placed on your spine while sitting. Forcing myself to get up with a timer made a huge difference with my back pain. Before, I was at my chiropractor's office at least once a week.
You can also elevate your feet, which will (naturally) force you to sit more upright. In the past, I've used some books (wrapped in an old plastic garbage bag to keep them safe from mopping). But now, I'm used to it, and it's enough for me to just put my feet on the chair's wheels.
