I follow based on flight timings. For red eye flights, PJ. For Malaysia, just normal rompers will do. Can bring along a small blanket (in case on board doesn’t provides) or just use your own jacket/top as blanket.
Short flight just normal short sleeved rompers with pants. I'll just cover baby with blanket if i see tt she's feeling cold. Unless it's more than 3 hours flight, esp at night, she'll be in long sleeved rompers.
If just short distance a short sleeve rompers with socks or as onesie or sleepsuit will be too warm after alighting from flight.