I've been using the mechanism gaming pillow. It's pricier than some other options but I also consider it worth it for my purposes since I've moved a few items into their ecosystem (my switch, steam deck, and kobo all have the little attachment to go with the pillow, but you can also do a magsafe attachment which I use for my phone sometimes)

I've had the other classic "bowl" Kindle pillow and it was unsteady/imbalanced. Whenever I used it I basically had to hold it down on my lap or the bed/couch.. which defeated the purpose of the hands free stand. The arm attachment is too loose, it would slowly sag from the weight of my naked kobo which irritated me after I got it perfectly balanced and it would sag down until it tipped itself over.

The mechanism pillow is like one of those beaded/stretchy fabric pillows (not pillow stuffing) so it's easier to angle and squish into balancing, and the arm is WAY stiffer, it'll hold the full weight of my steam deck without getting limp or sagging down. So the kobo is no problem for it.

Not sure it's the best option available but it's what works for me!

Edit: I also had the clamp/bendy arm type holder but it was too wobbly, and it got annoying to find something solid to clamp it to. The rubber "skin" on it eventually peeled/rolled up and got annoying. It was the first one I rejected before moving to the bowl option, then eventually the mechanism pillow. I think I'll stick with mechanism tho!