Portable chair or other device to avoid flopping over sideways

[INeedNewShoes]

DDad falls to one side when sitting in armchairs.

It’s not an issue at home as he has a winged armchair but at other relatives/friends’ houses he ends up hanging over the side of the chair when he falls asleep (which is a lot of the time).

Has anyone found any solutions to this when out and about at other people’s houses?

Bump - should have come up with a catchier thread title

I would take a pillow which can be put on that side, to support him.