My fiancee and I have been sleeping comfortably in a single bed for six months now
We either have both of us on our sides (if I'm behind her I'll put one arm under the little crook in her neck where it won't fall asleep and the other over the top of her, like I'm giving her a hug... she hasn't yet found a place to put her arm under me if I'm in front so she just tucks it up in between) or with my lying on my back and her on her side with her head on my chest.
God I love it too... I'm glad we don't have a bigger bed, I just love falling asleep so close to her.