I have the Ergon version of those. They work well, but more from a wrist support perspective. There's also things like TOGS (thumb over grips:
https://togs.com/ ), those might help. I don't have arthritis so I can't comment on what is likely to work for you.
I wouldn't hesitate to at least try adjusting the angle or spacing of the shifters. That's free and only take a minute or two. Many bikes come with the shifters and brake levers pointed too far down. You want them to basically be inline with your arms/wrist when in your normal riding position. There's also nothing wrong with cutting the bars down by 5-10mm on each side. Adjust the grips and shifters, test and then cut.