Have you tried correcting your posture? I find it very uncomfortable and eventually it slips my mind. Today I am going to make a conscious effort to think about my posture.
In fact right now my shoulders are complain and i feel a slight awareness in stoach - its hard to explain. I know yoga is recommended to help but I have tried some videos and I can't think how an overweight person can most of those poses.
Pillow Posture
Place a pillow behind your lower back while you’re sitting at your desk to avoid slouching, decrease lower-back pain, improve posture and increase abdominal strength. Even better, it sounds so comfy. Who ever said you couldn’t get in shape just by sitting there?
(From article: Got 5 Minutes? It's All You Need to Get Fit: http://www.neversaydiet.com/slideshow/5-easiest-exercises-ever)
"Good posture makes one look taller, slimmer and more confident. From a health perspective, correct posture has been shown to speed recovery from episodes of low-back pain and help prevent recurrence. In fact, there may be nothing more important than good posture to prevent many aches and pains resulting from undue stress on joints and muscles." (http://www.orthone.com/one/services/spine/posture.cfm)