Having the right seats really make a huge difference in any car. The good news is that the seats that are used on the venerable Porsche GT3 or even sport seats from a different Carrera can be easily swapped back and forth. The GT3 seats are sportier, are more supportive, and have the appropriate cutouts in order to accommodate an appropriate multi-point racing harness. The GT3 mounting brackets also have a lower bar to accommodate a sub-belt too. Stock seats, particularly the power ones, weigh a ton, and the GT3 seats typically save about 30 pounds of weight or more over the stock seats. At about $3,000 each, genuine Porsche ones (with the Porsche crest embossed on them) are not cheap, but they are definitely the coolest seat around. Aftermarket ones and OEM Recaro seats can be had for less--replicas tend to run around $1,500 a pair.
In order to mount the seats to your car, you need a set of seat mount brackets. Brey-Krause manufactures a dizzying array of brackets and adapters for race seats and is the obvious choice when selecting a seat bracket. The parts required for installation depend upon the seat, the year of your Carrera, and whether you plan to mount the seat to the floor or to sliders. In general, I recommend the adapters that allow you to mount the seat to the stock non-power seat sliders. The GT3 seats also tend to sit lower in the car than stock seats or aftermarket race seats, which is great if you're tall and your helmet tends to stick up too much in the car. The GT3 seats should be a direct swap into the 1998-2008 Carreras with no air bag computer programming required.
If you install an aftermarket seat in your car, you will initially have a problem with the air bag computer giving you errors. You need to reprogram the computer (using the Porsche factory PST-2 or PIWIS) to ignore the error signals. The late-model cars with side air bags in the seat also need to be disabled. If you use a five-point harness with your seats, then you will need to disable the seat belt sensors. Finally, you need to turn off the Automatic Weight Sensor (AWS) for the passenger seat. If you take your car to the Porsche dealer or an independent with the PIWIS tool, then it should take about 20-30 minutes for them to reprogram the air bag controller for you.
This photo shows a set of after market carbon fiber seats being installed in a 996 Cabriolet. .