I think that greatly depends on the person. I love a nice firm bed as long as I have a small blanket or decent pillow to tuck under my head, but my wife needs a super soft bed that she can sink into and 3+ pillows otherwise she doesn't sleep and is sore the next day.
Well, it is an odd beast. If I sleep on a firm mattress, I wake up with all kinds of soreness and pains. It isn't the same as sleeping on the ground or a Japanese style bed. I was always a soft mattress kind of guy. For my wife, it didn't matte what kind of mattress it was, it was bad. The tatami mat+futon has really helped her.
The shocking thing is, that when you really dig down into it, there isn't any real research on how bed types affect sleep, other than marketing/propaganda from companies and anecdotal evidence like mine. So mileage does vary.
At the end of the day, I think we consider our PCs experienced adventurers used to this kind of thing, especially a heavy armor class. This is the kind of person he is more like the battle worn soldier who could sleep in the middle of an active warzone in a foxhole. Sleeping in armor likely will have little effect on them. Hygiene issues are more likely, but I would consider those similar to having to eliminate bodily wastes, as in something usually skipped over in stories.