Before World War I, there was no such thing as a Singapore Malay community. What used to be loosely grouped as "Malays" were Javanese, Boyanese, Minangkabau and Bugis. Then there were the Penisular Malays, mostly form Johor and Malacca. And the Rhio Malays. Each had their distinctive style of clothing although the unifiying basic garment for all of them was the Sarong
The population in the early years of Singapore was very transient. Marriage, when it took place, was also confined to unions within their own racial group. What they had in common was their religion, Islam. This gelling of the different Muslim groups into one community only came about around World War II.
Before this, each community had their own kampung (village). The impact of the war forced them to cross ethnic lines and slowly that one rubric known as the Singapore Malay came about. The war also forced some of the women to go out to work in the factories. Their clothing (baju) had to be simplified and became more uniform due, if nothing else, for a severe shortage of fabrics.
But after the war, the sleeves of the ladies' baju became long again. So long they were folded back and that became a style-- the baju kurong as we knew in the 50s.
However, came the time for celebrations and each group of Malays still kept to their original costumes. Mind you though, the everyday basic dress of each Malay group was not that different from each other. And overtime, distinctions blurred.
Today most under 30 Singapore Malay women are English educated and working. Some are professionals and serious about their careers. These women would, like the other race, wear mostly western attire at work and change into jeans and tee-shirts for play. A good number of them would still cover their heads with a scarf, selengang or serkup. They would also sometimes wear a slim-fitting baju kurong to work but never the Baju Kebaya . The latter being much more restricting, are reserved for special occasions.
Unlike Westerners with their constricted clothing, the Malays, with their loose clothing, seem to prefer a "comfort-first" approach to dressing. A most sensible response to the weather. The sarong was worn by both male and female and so was the baju kurong. But the length of the baju was much longer for the female than the male.
The basics for man was normally the seluar (pants) and the baju (shirt). Headgear was optional ; they could wear either the songkok, the serban (turban) or tanjak. As for footwear, it was either the capel or they would be bare-footed.
The basic dress for women comprised the kain(sarong) and the baju(loose tunic). With this they sometimes wound a selendang (a flimsy scarf) loosely around the neck. with the ends dangling in front. Or if they chose to cover their head, they would use a tudung. A selimpang, a length of contrasting printed fabric, is also used instead of a selendang.
It was very likely that the Muslim Indians traders who brought the trousers to the Malay Penisular. In the early days, trousers were baggy garments, falling to just below the knee. Later, came the Achinese style of trousers: legs were close fitted but seats were rommy.
Men of rank and royalty wore trousers woven with gold threads. Such style prevailed until the 19th century when the long loose trousers of the Chinese or European together with stockings or socks, exerted their influence.
Malays who abandoned their traditional pursuits like fishing and hawking and joined the various uniformed services got used to western-style trousers. For lazing around, most would have worn the sarong, at least they did 20-25 years ago but since blue jeans and tee-shirts became universally popular, it is mostly the older ones who wear the sarong.