There was another thread similar, asking about what to wear going from cold UK to somewhere hot. I'll link if I can find it.
I always take a thin pashmina/shawl. I wear it as a scarf in the UK, rolled up it can be a pillow, wear it over my shoulders on the flight if chilly, and also use it as a long skirt, if going into a temple or somewhere that don't allow shorts. (More so in say Thailand).
Singapore is very humid! It can be a shock when the doors open at the airport! If leaving a cold country, I layer up. T-shirt, long sleeve t-shirt/top, maybe a cardigan and this light jacket. Its light but warm and folds up to fit into a small, backpack pocket. https://www.marksandspencer.com/feather-and-down-quilted-packaway-puffer-jacket/p/clp60683427?color=BLACK
Sometimes I take shorts or a skirt to change into on arrival. I often get cold on the plane too.
I always take those thin, hotel type slippers. When I get on board, I remove my shoes and socks and put on a thicker, bed type sock. I then use the slippers whenever walking around the cabin. The toilets always have suspicious fluids on the floor, so I would never walk in just socks or barefeet! 😝
In addition to trying to sleep on the flight, where possible, I try to get into the time zone a few days earlier. I can't recall now which way, but I go to bed say 1hr later(or earlier) and set an alarm to get up, then 'try' the next night to go 2hrs later/earlier etc.
On arrival, get into the sun. It too helps with your body clock. If you absolutely must nap- set an alarm and limit it to 30mins or so.
Singapore is fabulous, clean and the franca linga is English, so very easy to get around.
As a child, the night zoo, and day time, was amazing!