What about Ryan air (pack light). My daughter & I used it to go from Frankfurt to Venice on a cruise. I could imagine how we would plan it all (or where to go, so much to see) as I wanted to visit while she was there. The cruise was awesome. Caught the ship in Venice, then to Taomina Sicily, Rome, Florence, Monte Carlo, Ajiccio Corsica France, Naples, Dubrovnik Croatia.
We had an awesome time & I had never wanted to cruise but it was great. No worry about where to eat or sleep. I'd like to go back & right now there are cheap flights from the US to Frankfurt but not on a cruise. While my daughter was in Europe she traveled by train & got to visit almost every country. Have an awesome trip!