middle age
in the mid age, bed is a very expensive item, most of family only have one bed in home, so, the whole family will have to sleep on a same bed. in the hotel, sleep at the same bed with strangers are also a normal thing.
16-18th century
in the 16th to 18th century, people don't need to sleep in one bed with others anymore, they now have their own bed. the bed in this time period have many layers of mattresses, and people will wash and change them everyday, which cause woman in the family spent lots of time for it everyday.
now
today, because of the improvement of the techonology, most of bed only use one mattresses, today's mattresses can provide more stability and support to the sleeper.