I believe the turn of the century is when it started shifting in a big way in the United states, but this is a particularly finicky thing to measure and really contingent on geography. In the 1880s, it was still routine for a male visitor to a house to share his bed with other male residents in most places in the US. I am pretty sure it was unusual in by World War 2.
That’s mostly a function of society becoming affluent enough that people could afford to have a spare bed for when visitors come over.
That’s mostly a function of society becoming affluent enough that people could afford to have a spare bed for when visitors come over.