The setup that I adopted 15 years ago and still use today is the "bar desk". It's a standup desk that's positioned in such a way that my elbows rest naturally when I'm standing. But instead of a fancy mechanism to make the desk go up and down, I have a saddle stool. When sitting on it, my head is at the same level as standing, and my spine is straight. (Key point is monitor position.) What I like about that is I can…
One issue though is the lack of a back on the stool. You can make the case it’s a Good thing but when I really need to concentrate if I’m tensing muscles in my back to keep straight it won’t be the same—or you can slouch which also isn’t perfect.