We did Nuremberg to Vienna in 2018 (first week in December). I found that the important thing was to plan for layers. The coldest I've ever been was sitting in the Cathedral in Passau waiting for a concert to start. One thing I do recommend though which may seem odd..... waterproof rain/snow pants. I had nice ones, not the slick fabric We had drizzle off and on through out our walks/tours. I got lots of jealous comments about them. I could sit anywhere, and never worry about getting wet. No uncomfortable wet pant legs. I also brought my down jacket, which was only water resistant, lightweight rain jacket and wore them at the same time. Kept my down jacket dry.
