Can I raise the ceiling Without having joists visible
If I am reading your post correctly you want to raise the ceiling  by 600ml's which,  if Google is right, that comes out to 23.622In. I don't see that happening without a total rework of the ceiling. You have a better chance of lowering the bed at the bottom, but you are going to lose that space. Take pictures or give us a drawing with dimensions of the room and lets see what the group can come up with.