Bewitched was based on a movie called “I Married A Witch” with Frederic March and Veronica Lake, early 1940’s. Very funny movie.
My hypothesis is that the movie "Bell, Book, and Candle" (with Jimmy Stewart as the beleaguered "mortal" and Kim Novak as the witch) provided the actual impetus. The film came out in 1958, and probably prepared the way for the tv show.
The film even has characters which could be viewed as forerunners for the "Aunt Clara" and "Uncle Arthur" characters on "Bewitched."
Regards,