I'm also old, and have used one of the Thermarest chairs for years. I really like them - they're a good balance of light weight, function, comfort, and durability. If you don't want your legs on the ground, and if you use a full-length Thermarest, they make a "lounger" that covers the whole pad and never needs to be removed; it puts length out under your legs.

Try Campmor if you want an actual chair - they tend to carry stuff like that. I'm a little curious: what kind of tent are you carrying that would be tall enough and wide enough to sit in a chair? (One other consideration: will the chair legs abrade the tent floor?)