I just bought a trackball but it has intolerable sticktion.

Trackball gang is a lie!

The two I've used are the one in the image (it's from Anker, I forget the model) and Logitech's MX Vertical (they have a second, smaller version if the original is too big). I've been maining the Vertical the past 4 years for work and personal use.
Both have pros and cons:
Anker is cheaper. ~$35 vs ~$80. Also has a built in slot to put the receiver in when not in use.
It curves with your hand more than the Vertical.
Anker uses easily replaceable AAA batteries. Usually lasted me about 3 months before I needed to swap them. I only used it for work though.

The Vertical can connect to 3 different devices (1 dongle, 2 Bluetooth) whereas Anker is limited to whatever the dongle is connected to.
The Vertical is made of better feeling materials; like a rubber for extra grip vs hard plastic with the Anker.
There's a USB C port to charge its (not easily replaceable) battery.
Edit: Vertical won't go to "sleep" like the Anker will. If the Anker isn't touched for X minutes, it will go to sleep and you'll have to click one of the switches to wake it. Otherwise moving it won't move the cursor. Not that huge of an issue, but definitely annoying if you don't know what's going on.

However, there is a design flaw with the Vertical. Logitech run their wireless mice at very low voltage and current to save on battery. That's how they get a 240 mAh battery to last for around a month of heavy use.
The problem with this is you need to use particular switches, otherwise corrosion starts to build up on the connectors. This corrosion leads to incomplete or missed clicks, phantom double clicks, or it's impossible to hold a click.
From what I remember, standard switches are designed for 5V, since that's what wired mice normally run at. But modern wireless mice operate around a tenth of that. Logitech never made the switch (heh) to switches rated for that low voltage. At least not when I bought mine.

My Vertical had that issue. And rather than buy an entirely new mouse, I went in, desoldered the old switches and replaced them with new ones (I think I went with Kale's light blue switches). I did that in summer '22 and haven't had any issues since.
The rubber material is also showing wear and tear where my fingers sit, but that's just cosmetic.

I got the Anker one for my mom holiday '22 and she's been happy with it. It helped the discomfort in her hand.
Both mice improved the stiffness in my right hand, so either one will get the job done. I will also say that there is a bit of an adjustment period. Surprisingly, changing the angle of your hand kind of throws you off and takes some getting used to. Before my office went remote, my coworkers would avoid using it because it wasn't easy for them to switch to for just a short period of time.

Hopefully this info is helpful. I can try answering any questions you have on them, but those are the only two I have experience in.

Edit 2: Phrasing