I always keep a straight posture. Either I'm standing, or I'm sitting with my back straight. I make sure I don't slouch, because that's what causes pain. Used to feel natural to slouch, but now it feels natural to puff my chest out. Also, walking on a treadmill while reading makes it impossible to slouch.
With my wrists, I'm not sure I get it. Surely people are not actually typing all the time? I spend a lot of time looking at the code by using the touchpad. A lot of slidey-two-fingers to scroll the text. But also I hardly type much when coding. I type in something, let smart complete fill in the line, hit tab. But it's not even that much text to type in. Most of the work is looking at things and thinking. Perhaps it's the height of the table, I have a movey-up-down table that I adjust so I'm not uncomfortable. But basically I never have wrist pain, whether I'm standing or sitting.