Here's a bunch of links to all sorts of mount product pages and videos... I've tried to link to all the different types of designs I have seen myself so far, although many of these concepts are very similar.
Probably most important is to be stable, then adjustable. Portability isn't important for me, but ability to go from sit to stand is, which is why I would probably rather attach to the desk instead of the chair. For me would be nice if the mounting solution could extend outwards a foot or two away from the desk to approximate armrest position and emulate chair attachment, while maintaining the ability to adjust position freely throughout the day. That's why I think something like an articulating arm or gooseneck is appealing, but am worried about stability and wobble when typing. In the end, I'm guessing a short and permanently fixed mount is the most reliable solution, but it would be to be free-moving and highly extendable like those:
That last one might be awesome but rather expensive.
Some of these online stores have many more solutions than the few specific ones I linked to. Some of the sales websites are from the 90s and are hard to navigate, but if you poke around more you might find other possibilities (was just skimming these sites and linking things that looked interesting).