his/her chair
Il reposa son stylo et se laissa aller contre le dossier de sa chaise.
He put down his pen and leaned back in his chair.
Elle s'est levée de sa chaise.
She got up from her chair.
Lorsqu'elle a appris la nouvelle, elle a bondi de sa chaise.
When she heard the news, she jumped out of her chair.
Il reste assis sur sa chaise, à rien foutre.
He just sits there in his chair, doing fuck-all.
— Gangs of Wasseypur : 1ère partie (2012)