Rules of an infant carseat....?

Me and my bf is debating the law of proper carseat setup in a vehicle. I have only a ford ranger that has to seats and a console seat and I mentioned bringing the baby home in the carseat with base in passenger side and me in the middle. He is saying that she is safer in the middle and without the base and just strapping the belt over the carseat in the belt slits on the carseat. What is the LAWFUL way??