The research is pretty overwhelming - huge gains in worker productivity happen by simply standing instead of sitting at a desk. There are many tools now to help you be able to both stand and sit at the same desk, including some tools for what you stand on. (warning: I have not used the Wurf board myself; time and research will decide if it is a good idea; check out the short video the web page has; I think I'd give this one a try.)
My office is currently in constant flux and so I use cardboard boxes to get 'standing height' on my computer, and I've known people to use unopened reams of paper and books shelves behind their desk to accomplish the same thing. I can work much longer at the computer when I'm standing vs when I'm sitting - no contest. You have to find a proper height for looking at the screen and hand height for the keyboard. And I know a lawyer who bought a standing desk with a treadmill built in because he was trying to beat the early afternoon drowsiness. He was initially the laughing stock of the office. Now, they fight to use his desk when he is out of the office. (The better treadmill desks restrict the speed to the slow side of things - the purpose is NOT exercise, it is adding movement to gain the boost of chemicals the muscle movement produces. And the treadmill desk can also just be used as a standing desk when that is preferred.)
And, by the way, productivity studies also show a 60% increase in creativity just by adding walking breaks at work.