The main difference between first and business class these days is the small private cabin with dedicated crew and a schedule that is based on your needs rather than the cabin as a whole. Flying SIN-AU overnight is a short flight - 6 hours 30 minutes (or less in some cases). In business class the lights are on (even though dimmed) with the breakfast service around 2 hours before arrival. In F the cabin is quite and blacked out until they wake you 20 minutes before landing (with a hot towel and strong coffee
). F is all about you. J is still about you, but everyone else at the same time
Both cabins have flat beds, but the size is markedly different. F doesn't usually have an cubby holes, cut-outs or tubes for your feet. So you get a better, unrestricted, sleep.