My train from Paris to Toulouse was a TGV (= Train of Great Speed), leaving the station Paris-Montparnasse at 12:28 and arriving Toulouse-Matabiau five and a half hours later, at 17:57. There was one brief stop in Bordeaux along the way.
When I left Toulouse a few days later it was on a TGV train to Bordeaux, but this time I traveled first class because when I booked there was a special deal available on the SNCF website for only 25 Euros.
Both the French and the German railways have complicated price structures with constantly changing prices, so all I can suggest is to look at the website and see what is available.
Actually, I didn’t find much difference between first and second class. Both are comfortable but a bit cramped, since they try to fit as many passengers as possible into a small space.
In Germany I used to travel first class quite often (back in the days when my textbook publisher paid for the tickets). First class in German trains is somewhat roomier than second — three seats in each row instead of four — but what you are mainly paying extra for is to be travelling with well-off people of your own (real or imagined) social class rather than with disreputable characters like me.
My photos in this post are from 2014. I revised the text in 2019.