After much research, I bought a Rick Steves Convertible Bag several years ago and have been quite happy with it. I have used it a half dozen times, for personal and business trips and have been very satisfied. it replaced an inexpensive rolling bag. One of my goals was to avoid rollers; I wanted a bag I could wear as a backpack or carry as a suit case. I also liked its light weight and lack of structure.
But instead of using the packing cubes recommended with it, I found a different solution: a hanging collapsible set of "valet compression shelving." When I bought mine, they were $26.
I pack my underwear, socks, folder shirts, t-shirts and folded or rolled trousers in them. When collapsed, they provide the structure to the bag that the packing cubes otherwise would. I fit in shoes and other items on the side, or in the various compartments in the bag. Unpacking is a snap; I just pull out the shelves and hang them in the closet. Voila! I don't even take out the items, except perhaps the shirts if they are business shirts I need to iron in the hotel room. the same goes for a business jacket if I need one; I carefully fold it, keep it in the large front compartment, then iron it in the hotel room if I need to.
No matter how long the trip I pack for this way, I have never been caught short, although I have sometimes have items I didn't need. (On business trips, I usually bring a small leather briefcase-type bag for my laptop, electronic doodads, work papers etc., although I have the option of leaving this behind if I wish--the convertible bag usually has enough space.) If I'm there longer than a week, I just do laundry.
Admittedly, I have never traveled in really cold weather. But in that case, I would layer rather than bring a heavy coat.