If the problem is bad posture while sitting at the computer, you could try removing your chair's back and armrests. Once I learned how to sit right (with Alexander technique), I discovered that back and armrests are like magnets for my body, and they also make it quite easy to sit in a bad posture for a long time before noticing. Without that support though, a bad posture become uncomfortable much faster, and I soon notice and straighten up.