My DS is having his first sleep over he's 9.5 years and his friend is a little older at 12 (very young 12 though).
DS has a 3/4 bed but Im guessing unlike when I was a girl we would top and tail or share the bed when we had sleep overs etc...
Ive suggested that my DS offers his friend the bed and I make a bed up on the floor for him. Also we have a single futon mattress would this be adequate. Gosh I sound rubbish dont I :)