Baby car seat

Hi mummies, we don't own a car, however, most of the time we will be taking taxi/grab car. Is it mandatory to get baby seat? Or can I just get grabfamily as they provide booster seat for kids 4 to 7 years old. But what about NB to 2 years old as I will be giving birth in Sept 2021. Since I have a tula carrier, can I fasten my seat belt first and then fasten the baby onto the carrier to myself?