Darkness. Complete and utter darkness. I think people really undervalue darkness. I can't sleep unless I'm either exhausted, or it's pitch black. You can guess which happens more often >W<
I'd want a really, really soft mattress. I've got a bad back, so it's a lot more comfortable when I don't have anything pushing against it.
And plushies. There must be plushies. A bed is not a bed without plushies.