@alex It's not really *designed* to be used this way, but I've found it pretty easy to hold the Logitech MX Ergo in my hand while using it - it's a trackball so it doesn't require a surface for use, and although it's not the lightest device, the shape and weight distribution are sufficiently good that I don't usually need to make much effort to hold it.
(The magnetic baseplate can be removed to significantly reduce the weight, though it makes it feel a bit unbalanced in weight)
I previously had a Logitech M570, but that one is really too slippery to hold like that comfortably.
@alex I should note that I sometimes use it this way for RSI reasons, when I'm just scrolling through and reading things, so that I can lean back without needing to have my arm and wrist in a fixed desk position.
That does mean I usually rest it on my leg, kind of on its side, while holding it. I don't know if this also works for your specific accessibility needs.