I think even if you're in a chair, and you're sitting up straight with good posture, maybe hands on knees.

哪怕只是坐在椅子上，坐直并保持良好姿势，也许双手放在两膝上。

普林斯顿公开课 - 人性课程节选

The Uprightsleeper looks like a neck brace the kind worn to immobilize the cervical spine after a traumatic injury (although it "makes no medical claims") and facilitates sleeping while sitting straight up.

WSJ: The Best Travel Pillows: Desperately Seeking Slumber

Whenever he came home, he found her in the living room, sitting up straight on the couch.

NEWYORKER: Creative Writing

Miller was despondent, sitting at his locker and staring straight ahead for several minutes before speaking with reporters.

WSJ: Frattin lifts Maple Leafs over Sabres 4-3 in OT