I had to look at your profile to see that you were female - yes, it makes a difference in the answer! Your key challenges will be cold and/or sloppy weather. You'll also be outside a good part of the time so you'll want more protection than others that want to sit by the fire.
One of your key pieces will be a good pair of waterproof shoes/boots. I like to use unlined waterproof dress snow boots and add in layers of merino socks as needed. Mine are Merrell, but there are a lot of nice choices out there. I can wear the boots with tights and a dress, under my pants, or with my pants tucked in. The snow boots have a better tread than regular boots. Look around and you'll see some that are hard to distinguish from normal boots. If you don't want knee highs then think about ankle boots. These are trendy right now.
The key for everything else is layers and temperature extender pieces. A nice 3/4 sleeve scoop neck silk long underwear top hides under street clothing. Leggings work under pants or dresses. A few camisoles or tank tops add variety and warmth. A merino sweater is a good layer over your clothing. Cardigans work well because you can wear them open or closed - that is really nice when you go inside. A scarf or two adds variety and warmth at the neck.
You may want to bring a puff jacket or a fleece as an additional layer. Top it off with a nice packable waterproof trench.
The layers let you control temperature for the weather.
If you know beyond doubt that you are traveling in really cold weather you can bring a winter coat and wear it on the plane. That said, I've found the layers / sweater / waterproof shell to be sufficient down to around -20 F.
Bring a good pair of gloves / mittens and a good hat.
Lounging: I like to use a t-zip base layer top that I can add to my layers as needed if I go outside. I like to use yoga pants for my bottoms. This outfit works well for skiing too when combined with the layers above and the addition of a pair of very light weight waterproof rain pants. Bring a pair of slipper socks for cold floors. Sometimes I pack a pair of silk long john leggings too for outdoors activities and for sleeping.
Other clothing: I'd recommend a dressy flat as a 2nd set of shoes (packable, slip resistant).
So my coordinated clothing packing list looks like this:
2 pairs of pants, 4-6 tops (2 shells and 2 long sleeve minimum), 2 sweaters, 1 dress, 1 legging, 1 silk long underwear top, 1 t-zip base layer top, 1 yoga pants, 1 stockings/tights, 1 fleece, 1 waterproof trench, 1 pair metallic ballet flats, 1 pair waterproof dress boots, 2 scarves, 1-2 gloves, 1 hat and at least 4 pairs merino socks. Two lightweight pairs are better than 1 thick one as they dry faster when washed. 4 pairs lets me do 2+2 alternating between days.
This is sufficient for a 3 week trip to a cold area.
BTW, I will wear my long john top under my sleeveless shell and a sweater. No one can tell. If it gets too hot I pull off the long underwear top and put it in a zip-lock in my purse.
All of the above fits in a single carry on bag (no need for a tote). There is room for my cross body bag purse.