Recommendations for lightweight car seat for those who don't drive

Hi mummies, do I need a car seat for my newborn if I don't own a car?? firsttimemom any recommendation for affordable lightweight portable car seats for newborn onwards? We don't own a car but felt it might be good to have esp when we travel in parents car or private hire car. For mummies who do that, could you also share if you just lug the carseat and carrier out? ie no need for stroller since there are so many things on hand already. #pleasehelp #advicepls #firsttimemom