The mic should be placed at roughly ear height from the seated position(s) however since it is pretty much an omni-directional mic precise aiming isn't critical (but it should point up, roughly). A tripod is nice but if one never has use for it ever again I wouldn't recommend bothering to invest in one and would instead recommend temporarily duct taping the mic to a broom/mop pole or similar such stick and resting that from behind the chair such that the mic will be held at the ear position facing roughly straight up.
Audiophiles like to obsess about things however [like whether their turntable shelf is leaning in one direction by a degree or two] so super exact microphone placement with a super rigid, sandbag damped tripod is exactly the sort of thing they'll cling to in this day and age. It's obsessive nonsense .
If people expect to apply microphone calibration repeatedly, like say because one decides to rearrange the positioning of the remotes on the coffee table or wear a plush sweater while watching a movie on some days (
), I'd recommend buying a dirt cheap tripod