Much of the muscle and joint pain in the thoracic spine (mid and upper back) can be released with a few minutes of simple foam rolling at the end of your work day. Foam rollers can be found at almost any sporting goods store or on Amazon for less than $15 dollars and are well worth the investment!
The one that I like and recommend can be found here on Amazon. This is the 24" length, but you can get them in varying lengths to suit your personal preference.