I have a comfy stool to sit in at my standing desk. I've found that without even thinking about it, I stand when producing, and sit when consuming. For example I'll sit and read some documentation or sample code, then stand to write my code. Standing felt quite natural after a day or two.

As for productivity/quality of work, it's not worse. For quality of life, it's much better as I don't feel as drained at the end of the day.