The safest way to travel in a taxi with your little bundle of joy is to use an infant car seat without the base (such as Maxi Cosi), and properly install it using the taxi seat belt. Here's a great video from America's Car Seat Lady on installing your infant car seat in a taxi. You'll notice in the video, that Dr Baer engages the auto-locking feature of her vehicle's seat belt. Dual-mode seat belts are uncommon in Singapore (very few taxis have them, but some Uber/Grab cars do). To lock a standard seat belt (ie. one that only locks in an emergency), use one of our taxi-friendly locking clips.
If your child has outgrown their infant car seat, then consider a taxi-friendly toddler car seat such as a Cosco Scenera NEXT (rear facing) or Combi Coccoro (forward facing).
Once your chid is old enough for a booster seat, the RideSafer vest (version 2) is an excellent next stage. It's not a car seat, it's a booster seat alternative - but it has a number of features which make it safer than a standard taxi-friendly booster seat (eg. Trunki Boostapak, Mifold, BubbleBum).