When it is cold I wear plain black, grey or navy trousers for best. Land's End do a good range and they are reasonable cut and quality. As for style, I am short and dumpy so I wear slim legged trousers but taller people can bring off the more fashionable wide leg trousers.* The inevitable Marks and Spencer also do a good range.
I still think that, for me, dresses are more comfortable in the warmer months and I really don't look good in shorts or cropped trousers.
I hope this is of some help to you.
*For older people wide leg trousers can present a tripping hazard especially if they cover your shoes,