I can recommend the Expedition coats. I have worn them in Norway, in January, in a blizzard. You can go out in just thermals and a tee shirt with one of these on top. They are really well insulated. They have double zips and side vents so you can walk in them. The wrists have proper ribbed cuffs to keep the weather out. They are windproof and waterproof. Just double check your measurements. My only negative is if you have large upper arms, you may need to size up. You should be able to get one for around £100, don't pay full price, there's always a discount sale of some sort every week.