for -10 and above, i personally use the following, otherwise too hot indoor..
a normal short sleeve t-shirt, uniqlo airsm or any other cotton t-shirt (this is replaced by a cotton business shirt if work), a long sleeve wool/cashmere sweater, can also be from uniqlo and if work only, my wool business suit and finally then a canada goose parka as the final outer layer(this is the one that is most impt).
cashmere scarf for comfort, otherwise a wool scarf works too but i do recommend cashmere, feel more comfortable..
gloves from dents. they ship to sg without vat and it is very worth it.. mine is cashmere lined deerskin.
a wool cap if needed but i usually just use my parka hood.
for bottom, first of all, of course my usual underpants/wear, a long legging if very cold but i skip this if not outdoor most of the time, can be from uniqlo but i personally like merino wool or cashmere, then jeans for leisure/offwork or wool pants if work
socks, get wool or merino wool socks, can be any brand, uniqlo also have, most impt is the material, then boots or business shoes depending on occasion. shoes must be waterproof so business shoes have to be genuine leather, dun use normal running shoes we usually use in sg, buy hiking boots is safest or shoes that is waterproof, your socks have to be dry..