Goodness me, it can be complex.
I would be thinking separates too - my first thought was a maxi silk skirt (in my head it was a dark tartan) with a coordinating fine gauge knit sweater (maybe in forest or burgundy) with hairup and cool earrings. Or with a simple top with a well cut jacket on top (sort of riding style)
Then I imagined myself in the mountains, drinking mulled wine and fondue.....hiking with my cute wool hat...
I also think a cool pants suit would work, one that you could wear afterwards as a suit or seperates.
If it was unseasonally cold I think anything goes including puffers layered over the top.