I've been about 90% standing/10% sitting for the last several years, and while standing is great for me, the ergonomics of switch to and from my Aeron -- bought 15-ish years ago from a startup closing up shop -- felt less so.

I passed along the Aeron to my wife, who prefers a supportive chair and has also obviously been working from home, and got a Fully Tic Toc stool. It forces me to maintain something like healthy posture and keeps me at least gently moving throughout the day, and as a bonus fits neatly under the desk when I'm working rather than forcing me to find space elsewhere in my very compact home office.

I've found that for my 40-year-old knees and hips some sort of motion was necessary to keep from getting sore by the end of the day. The Tic Toc helps with that, as does the balance board I pull out when standing for any length of time. (The board is a Fluidstance, which is stupidly expensive for what amounts to a skateboard deck on top of a piece of bent sheet metal, but it feels a lot better than standing still and has held up really well so ¯\_(ツ)_/¯.)

Obviously this kind of setup isn't good for everyone, but I really like it.