Slightly more detailed itinerary...

Dec 14: fly BNE -> Singapore, O/night train to KL, Malaysia
Dec 15 - 18: KL, Malaysia
Dec 18: O/night train to Singapore
Dec 19: Singapore
Dec 20: fly Singapore -> Ho Chi Minh, Vietnam
Dec 21&22: Vietnam/Ho Chi Minh area
Dec 23 - Jan 12: Cambodia
Jan 13 - Jan 26: Laos
Jan 27 - Feb 7: Vietnam
Feb 7: fly Ho Chi Minh -> Bangkok
Feb 7 - 15: Thailand
Feb 15/16: fly Phuket -> Singapore -> BNE