It's always important to keep your child safe, especially when they're the youngest passenger in a vehicle. Aside from driving at a relative pace and keeping everyone with a seatbelt in-use, you will need to add an extra bit of protection for the kid in the back to stay out of harm's way. Given how small they are in terms of size or height, getting a car seat should at least help you better see them while also protecting their bodies from potential car accidents. As for the right seat for your child, it might be best to break down the two options available:
For newborn babies, rear-facing car seats would work well to better protect them at such an early age while also comprising of stroller features to prevent them from waking up as they're taken out of the seat.
For infants up to the age of 4, a forward-facing car seat would work well as they get older and slightly safer from the force of a crash.
For children up to the age of 8, a booster seat would be the right option when their height is 4 feet and 9 inches (on top of out-growing forward-facing car seats).