Seeking An Occasional Babysitter

My family is seeking a babysitter on an as-needed only basis to cover for when our full time nanny is not able to come in. We are trying to limit our son's exposure to many caregivers and would like someone who could become familiar. We believe it's important that our caregivers become somewhat like family because you would be taking care of ours. We want to limit how often our son has to say goodbye to people he learns to like!