Armchair is fine. If you go with "those armchairs", "that armchair", "the armchairs" or "the armchair", we'll be extra happy, it alleviates social dysphoria for our nonpeople folk.
It fits our general personality imo with the softness, being a support, and being relatively solid. We really like benches, they're our favorite thing in general; so: taking a name that's also furniture. It also just fits the being nonbinary which is fun :P
That being said it has one issue, that all names we've used have shared: the more it's used, the more it feels like a person name instead of an object name, and some of us really do not like being considered people. This is why we also go by "the armchair(s)" etc as a classic noun, also instead of only Armchair as a person name.