If you are hosteling and not camping, simpler would be a cotton or silk or (lightest) nonwoven nylon sleep sack, like the Cocoon sleeping bag liners. Most hostels forbid sleeping bags, claiming that they spread bedbugs. I also took a pillowcase with me when I was traveling in Europe after I found that, during the night, the sleep sack tended to work its way off the pillow that who knows how many other hostelers had slept on! A few hostels insist on your using their sheets, but most allow the sleep sacks.