If all you have is seat belt in the front, then that's all you have. What I suggest is that you push that front seat as far back as possible and rear-face your child for as long as possible. The Diono Radian will allow you to rear-face your child until 20.5kg, and yet it's very slim. However, it's also very tall, so I'm not sure if it can fit into the Kancil. Try to contact a shop and see if they'll let you just try it in your car before you buy?

Personally, I think you should try to find a car with seatbelts at the back. Even if you have to find third hand or fourth hand, seat belts at the back of a really old car would be better than a brand new car with no seat belts at the back. A full-grown adult flying from the back towards the front (because the full grown adult is not belted in) can injure anyone sitting in front. If your car only has seat belt for driver and for one passenger on your side, then no one and nothing should be seated at the back, to be safest.