I keep a "Dreamsack" in my travel bag and use it when the hotel sheets cause an allergic reation. My "Dreamack" weighs almost nothing and occupies very little room in my bag. I've even used it on overnight flights.

I sometimes travel with my mother and on a few occassions, the only room we could get would have only one king or queen bed. The "Dreamsack" allows us to share a bed but not share the covers (this may be TMI).