I have looked at the TVG-Europe.com site and there are serveral overnight trains. The best schedule for me leaves from Paris Bercy-where is Paris Bercy and how do I get there from St-Germaine?
Dianna, I'm assuming your closest Metro station will be St. Germain-des-Pres? If that's the case, take Metro Line 4 (direction Porte de Clignancourt) to Châtelet, transfer to Metro Line 14 (direction Bibliothéque François Mitterrrand) to Gare de Lyon. One word of caution regarding Châtelet Les Halles. It's considered a "super transfer station" and it's BIG. Your connection will probably involve a bit of walking through tunnels. I don't find it to be intimidating at all, but be sure to allow adequate time. From Gare de Lyon, it's a short walk to Gare de Bercy (across the street). If you're not hauling lots of luggage, it should be an easy connection. Happy travels!
There is one person who I rely on the most for information about trains from the UK towards France and Italy. He's The Man in Seat 61 and his webpage http://www.seat61.com/Italy.htm#Paris Gare de Bercy is a great start. If you scroll up after that you will see all about the night trains.... Happy planning...
You don't need to walk from Gare de Lyon to Gare de Bercy. Bercy is one stop beyond Gare de Lyon on metro line 14. Or you can take bus #87 directly from Bonaparte--Saint-Germain to Bercy.