TIP #1: If you do not want to use the lettuce, you can omit it. However, the flavor of a slightly bitter lettuce like escarole is perfect for the soup. It doesn't make the soup bitter at all, it's just a great merging of flavors.
TIP #2: The soup is best a bit creamy, so make sure to mash those beans down.
TIP #3: The wine rounds out the flavor of the soup. Make sure it is a dry wine. I buy a cheap white wine and that works great.
TIP #4: Serve with nice bread on the side