Ironically enough, actor Robert (Mike Brady) Reed was gay, though very closeted. I don’t hink he ever came right out and told Florence Henderson he was gay, but she did catch on. She has said in interviews that Reed was INCREDIBLY uncomfortable during those ‘snuggly’ moments.
According to Snopes, the first TV series to show a married couple sharing a bed was Mary Kay and Johnny was back in the 1940s. Ozzie and Harriet also shared a bed, as did Fred and Wilma Flintstone and Herman and Lily Munster. Lucy and Ricky Ricardo did sleep in twin beds, but they were pushed together.
It may be that The Brady Bunch showed Mike and Carol in bed together more frequently than these other shows, though. It’s my recollection that they were often shown talking in bed.
Excluding real-life married couples rules out most of the above, but The Flintstones premiered several years before Bewitched (although they were just cartoons) and The Munsters premiered the same year as Bewitched. But since the runs of these series overlapped, I don’t know which was actually the first to broadcast an episode showing a couple in the same bed.