1. buy from taobao or carousell (which is actually taobao but with 20% markup because Singaporeans don't use taobao). Iceland is going to be really expensive.
2. Don't need to buy $$$$$$$ brands. Don't be stupid, you're just going there for less than 1 month I presume. Not only Europeans have cold winters. China, Japan too have very cold weather, the people there don't die from cold weather, so there's gotta be something that works just as well. plenty of cheaper local stuff that works just as well.
Suggest you treat that set of "winter wear" as disposable - good enough to keep you warm, cheap enough to be discarded after your trip. It will save you the trouble of storage, especially if you don't use them more than once a year.
3. Paris is cheaper and more fashionable. That is, if you have the time to travel to the outlet mall area (La Vallée Village). It takes about 30 to 40min from CDG airport. That said, it's entirely dependent on luck, because tens of thousands of people flood that place everyday to buy cheap branded items. How cheap? 50% cheaper than the real outlet malls in JB/KL/Taiwan. Only Germany and and Austria cheaper based on my experience. If you want your stuff cheap and branded, suggest you try this.
4. Your idea of winterwear may be different from others. Some insist on having puffy jackets looking like baymax, some buy high tech material like dralon or heat tech where they wear less but feel warmer. If you want the hightech materials, buying online is better as you get better selection.