Florida

Is anyone out there well-versed in Florida vacation spots? My whole extended family is getting together in Orlando in late March for a few days, and my husband and I were thinking we might go someplace else in Florida for a romantic vacation by ourselves, either right before or right after the family thing. But I don't know the state well, and am not sure where to start looking. We'd want someplace quiet with good beaches, decent restaurants, pretty scenery. Quiet is important -- we don't need someplace isolated, but we REALLY don't want a whole crazy spring-break scene.

A friend recommended Sanibel Island, but I read something that suggests the average high temperature there in March is in the 70s, which isn't quite beach-weather. Any suggestions? (Would Key West be a good thought? Or is that too much of a party place?)