I think there's an older post regarding this, but i'm not sure where it is.
I'm fairly certain that i've figured out WHY the NPCs will all sleep on clothing items and pressure suits etc.
If you look at the attatched screen clip, note that the pressure suit i'm looking at has a "Cushion" tag on it.
I'll bet a paycheck that this tag is what allows NPCs to use them as a bed item, as well as other clothing items: