Consistent Babysitter Needed For 1 Baby In Los Angeles

We are looking for a great babysitter comfortable with babies for our 3-month-old (she will be three months in December). The hours are not the same every day and one day or two half days a week I will work from home so it also isn't complete full time. We would prefer a nanny who does not smoke and who has college degree. We have two older children who are in elementary school ao they aren't home during the day but it's possible I'll need sporadic help with them too.