Many compact cars are just that. Compact. Especially Compact sports cars, and compact economy sports carts, and economy cars from Japan. If you believe that the 2000+ Celica is tight, try getting in to an MR2-Spider, Scion FRS, or even a Lotus Elise.
Contact the guys at "Extend My Seat" - http://extendmyseat.com
They dont specifically list the Celica on their site, but they may offer more than what they advertise online.
If you take a look at a stock seat install pictorial, you'll notice that there really isn't a lot of room behind the seats to go back much further, but if you're able to find a replacement set of rails for the stock seats or an aftermarket set of seats that you like (with sliding rails and also uses a smaller foot-print/shorter) you could probably get an extra 4 to 8 inches from it.https://www.celicahobby.com/photos/celica/installs/inst_seat-install/