I just reverted your edit on the Bed page but I wanted to explain. I saw your post on discord - you are correct that Comfort, i.e. how much their comfort meter increases as they use the bed, is not affected by material.
But Rest Effectiveness, i.e. how long it takes them to sleep, IS affected. Stone has a 0.9x multiplier for rest effectiveness. What you deleted was about rest effectiveness. Not comfort.
Please don't let this dissuade you from future edits though