Married couples could not be shown in one bed. The I Love Lucy Show had Lucy and Desi with separate twin beds for example.
Bewitched changed that.
In one episode of the show "The Farmer's Daughter" the honeymooning couple were given a hotel room with two separate beds, not a single bed. Due to the requirements at the time when they complained they could not use the word "bed", instead they had to complain about the "wrong accomodations".
The late '40s show Mary Kay and Johnny had a married couple sharing a bed.
I was born well after the initial run of I Love Lucy but used to watch the re-runs as a kid. I remember thinking that Lucy and Ricky must always be angry at each other to have separate beds but at least Rick had a bed. When my parents argued, dad had to sleep on the couch.
FWIW, the first show to depict a couple in bed together was Mary Kay and Johnny in 1947, in which the two stars were married in real life.