I am looking at taking the night train from Vienna to Rome. There is something called a couchette carriage and then a sleeper cabin. What is the difference in these? Which is more comfortable for 2 people? Also it says the sleeper cabin has "a la carte" breakfast. Anyone know how that is different than the breakfast served in the couchette carriage? Also, what is the difference between "top" and "lower" on "your desired place" at checkout? Thanks!