Here you go:

CARES Child Aviation Restraints for toddlers

Occasionally my kid would be asleep when we were landing. I’d have to hold her head up with a hand as she would just loll forwards right over . Would have to keep wrenching her up too as she would often slouch down at the same time and the breast clip would end up at her neck.
Never regretted buying it. It is what it is. Just makes a safety belt a little safer for somebody who cannot take a proper brace position. That’s all.
Unless the seat has significant incline, it is not an option for a kid to sleep in.

Worked for us particularly as we don’t drive and never took a car seat anywhere.