During the 60s, as one person noted here in a different thread, most FM stations didn't really have set formats like they do nowadays (or since the 70s). They often had block programming, had formats like classical music or easy listening, or simulcast an AM sister station (which WTOS did not have). FM didn't have as much listenership as AM, because FM wasn't on car radios. It was at-home listening.
Having said that, I have no idea what they did between 1961-69. I do recall that at one point, they were freeform rock like WZMF (98.3). But, for most of the 70s into the mid-80s, they were WEZW, with a beautiful music (easy listening instrumentals) format that was typical of FM stations at the time and got monster ratings, albeit in very old demos. My grandparents listened to that station. Around 1985 or so, they started to add more AC songs. I remember being in the car with Grandma when "Axel F" by Harold Faltermeyer (the theme from Beverly Hills Cop) came on, and she started bemoaning all the weird music her station was suddenly playing. They did eventually go full AC.