Yesterday, after collecting the RV from the shop, we went to an office furniture warehouse near Reno airport. Looking around, we found a good, solid chair with a 350 pound capacity, high back, adjustable armrests, and a metal frame (not the plastic frame that the two now-failing older chairs had). The price was pretty good, too, as it was a former showroom display model. For less than the cost of most of the chairs at the OfficeBoxes, I got a better quality chair that feels stronger. Getting it into the RV was a bit of a challenge (for all that the RV is big, it doesn't have much cargo space), but we managed.
When we got home and wrestled the new chair into the living room, travelswithkuma tested the new chair out and pronounced it suitable for occupation. Kuma Bear can use the older chair (shown next to the new one) because he doesn't weigh so much and won't break the old chair.
The only fault I've found so far is that the new chair has less lumbar support, and inasmuch as I am in the chair ten hours a day, that could be an issue. I'll probably get a lumbar-support pillow. Otherwise, it's very comfortable and I'm glad we bought it.