Dont be silly. Use sarong.

Benefits:
1. Makes the child sleeps better because of the position. (felt more secure).
2. If the child sleeps better, will be healthier, hence grows better.
3. The parents will also gets more sleep.
4. The child heads will also be rounder.

Of course, you have this problem to have to take the sarong with you but who bothers cause you wont be travelling that much with a child too. Best, get a set at your parents and in-laws places.

You can train the child to sleep on the mattress later. Not difficult.