Ouigo, oui au non?

You are over thinking this for sure. I took that exact route 2 months ago. They email you the ticket 3 days before departure. You can either print out or show the bar code. There are no seating issues; you get an assigned seat just like the TGV or Intercity trains. It feels nothing like airtravel if you have the carry on size bag

If you're 100% sure about your schedule, and don't mind the lower comfort (tighter seats!) you can book Ouigo. The earlier booking is not much of a hassle in practice, tickets are print-at-home, just remember to purchase extra luggage if needed (yes, don't ask...).

But, say, between a 45 euro Ouigo and a 70 euro TGV, on a 4-hour journey I would be torn, and probably opt for the TGV. It's mostly a comfort-vs-cost decision.

I've used Ouigo. No problems. I paid the extra €5 for luggage, because it was still cheaper and I wasn't sure about the stated limit.

We did the Toulouse to Paris trip last September. If you’ve packed for airline carry-on only, the Ouigo is super simple...it’s basically just like taking a flight minus the time-consuming security lines. We as our tickets on my phone & scanned in very easily. There are size restrictions for bags but honestly we saw folks with hugely outsized bags getting on the train.

Be sure to check the train car position signs to know where you need to be when the train arrives. Let folks get off, then get on your car & find your seat. There are luggage racks near the door of each car AND behind the rear seats (so if your seat is near the back, take your bag & stow it there). There is room under the seat like on a plane but not as big. Fine for your personal item but likely not for your carry-on.

No food or beverage service on board so bring snacks or plan to picnic on the train, which is what we did. Seats are airline tight but the scenery outside the windows is lovely. There is A/C but it’s French A/C so cooler than outside but not cold (if you’re going during warm weather).

There is supposed to be wifi but I used data to get online because it was soooo...slowww... Games or books on airplane mode work, too.

With the time you’d spend at the airport to fly to Toulouse, you’ll spend about the same total time but you’ll save money on the Ouigo and get great scenery.

Had a reservation during the December strike -- Ouigo refunded to my credit card automatically.

I've used Ouigo multiple times. No issues.

For a Paris to Toulouse leg, however, I took an Air France flight from Orly to Toulouse. When the train leg gets long, I seriously consider a flight as an alternative. Generally, it's faster and cheaper.