If you have 90 velvet, you need at least 200 grams of velvet, which can keep you warm. Over the knee long down jacket to keep warm, velvet must be enough. If it is good down, 200 grams of down jacket is quite enough. A good down jacket will be more comfortable and warm, see whether the down jacket is warm or not, depending on the amount of down filling, fluffy and cashmere content, in general, if the three indicators are high, it will be very warm.
See what kind of effect you want, if light and light, more than 100 grams can be, if you want to pursue warm thick point 200-300 grams is also OK