Maybe it's getting on and walking on the bed that gives him pause. His old legs may be a bit unstable. Or maybe it is easier for him to *get up* from a hard surface than the underpinning of the bedding. In any event, having a older dog is sometimes filled with lots of new experiences for us as their guardians. Changes in habits, behavior, mood, etc. can be significant. One of my RB dogs developed doggie alzheimers. It was just awful to watch and to quite difficult to accommodate to her new needs which were many. As for Keito's sleeping arrangements, you've done all you can. Be content to let him decide.