Keep in mind that the car must have enough space for child seats so that everyone is comfortable. In my experience, taxi drivers near the airport don't have this, so it's better to book one of the popular transfers. When I was looking for a driver with a car on GetTransfer
https://gettransfer.com/en/directions/italy to go to the mountains, I specifically looked for an SUV so that the trip would be as comfortable as possible and there would be no unpleasant circumstances along the way. Among other things, there were both large cars like the Sprinter and business class cars like the Audi A6.