Hi NiagaraK,
Thanks for the kind words about the site.
Making sure your seat is facing in the direction of travel is very difficult to determine/choose before you get onto the train.
If the Thalys TGV train you'll be taking is a double decker (i.e. train cars have both upper and lower decks), see this
TGV Seat Map that may help you determine the orientation of your seat during the purchase process. Note, that I've never found a way to successfully specify my seat during the purchase process... I simply try to search for tickets at different times, hoping the seat I want is free.
You might be able to change your seat placement when you arrive at the train station by using a TGV ticket retrieval/purchase machine, although I haven't tried this myself.
I'm quite sure you can get the help of a SNCF ticket agent to change your seats at the train station, depending upon availability.
Hope this helps!
Ben