My son and I spent five weeks in Europe last year. We bought a Eurail pass before going over (have to plan far enough ahead to receive by mail, not sure how getting one when there works).
We took a night train from Paris to Zurich. We took several night trains on our trip, only sharing a sleeper with other people once, and one trip was inexpensive enough that we each got our own single-bed sleeper. We usually booked the beds just a couple nights before (or even the night before). We only got caught once and had to extend our stay in a town another night to get an available sleeper, but because we had a very flexible schedule, it wasn't a big deal.
Zurich was very expensive! I would have liked to be there longer, but my budget was happy that we weren't. We spent at least a few days in each country, except Switzerland, where we only stayed an afternoon.
We also took a train from Bayeux to London. We had a tour with the Cain Museum to see the Normandy beaches since we were not driving. While it would have been nice to have more time on the beach, the tour was great.
Also, if you're into WWII history and want to see the Maginot Line, I highly, highly recommend a side trip to Sedan, France. I believe we took the train there, but it may have been a bus (I'd have to look up my notes, but even if it was a bus, it was covered by our Eurail pass). We did a full day tour with Richard Tucker (Tucker Tours) and, because my son was under 18, we got a discount. It was just the two of us and Richard, quite a character! We got to do once-in-a-lifetime things with him. Bought lunch in a little store before we headed out, and then he drove us all over. He'll tailor the tour to what your interests are, and also mix it around so that you can be inside where it's cool during the hottest parts of the day when it's hot (and man, was it hot). He also recommended staying in the castle there, which was very reasonable. My son is a very serious sort, but this guy had him literally skipping down an underground tunnel! So much fun.
One big tip is to pack light! We each had a carry-on--one that was a backpack, one on wheels that also had backpack straps--from the Rick Steves website. I plan to use them every trip. In addition, we had a laptop bag. We wore lightweight, easily laundered clothing, doing some sink laundry, but also visited local laundromats for better cleaning. It was worth it to be able to travel light. We were in and out of trains easily, walking to the hotel was easy, etc. We even met people from our home state while in a laundromat in Germany!