TGV hi speed train

I've never seen numbers used for levels, but 1 should be the lower deck and 2 the upper deck. Upper is better for views but worse for access (by stairs) and for motion sickness (if prone).
There is no way to know which way you will face.

This seat plan from Set61 shows the direction of travel, but in parentheses "subject to change".
https://www.seat61.com/reference/trainseatplans/TGV-lyria-seat-map.pdf

The TGV Lyria trains are double-decked. Try for a seat on the upper deck. You can get a seat in all classes— including standard class—on the upper deck.

Re upper or lower deck. I opt for the lower because I don't want to schlep my bag up the stairs, and there often isn't space on the lower deck for upper deck passengers. P,us, your bag is out of your sight for the ride. Probably okay, then again......

A small lock on your bag deters anyone from rifling through it. And no one can steal your bag by taking it when the train stops at an intermediary station because the Lyria travels non-stop between Paris and Basel.

It does make 2 stops between Paris and Basel, at either Dijon or Belfort, and at Mulhouse.

Thank you for everyone’s reply. The train that goes from Paris to Basel is a TGV Oui not the Lyria I believe.
(I don’t know the difference ). I did want to book tickets on the upper deck, is there a place there for carry on luggage or only on the lower deck? I wanted the upper deck for scenery but had read it’s not good for motion sickness, could Dramamine help? Also, when I book on line, the cost is in Euros. Can I still use my credit card? Thank you so much.

Yes there are luggage racks upstairs in the upper deck. You need to take your luggage up a dozen steps.

As for motion sickness: are you severely motion sick in cars? If not, don't worry about it. Trains are smoother than cars.