This is something I want to experiment with as well. I tend to play music and shuffle, dance and pace around for movement while standing.

The thing that keeps me from going with a treadmill desk is that I switch from casual tasks (email, etc.) into highly focused work (coding, writing) seamlessly and for the focused tasks I prefer to sit most of the time, and even unplugging my laptop from speakers, power, monitor, etc. to take it to a chair or lower table just feels disruptive.

In terms of back health walking is hard to beat though. That's why I do my desk dances or even stand on unstable surfaces (a firm pillow or piece of foam in the simplest case) - to "diversify" my standing posture.