If you have a later model XJ, you can use WJ seats as a direct bolt in. You just have to swap the mounting rails from your XJ over to the WJ seats, and it's a direct bolt in from there. The mount holes on the XJ seat rails are the same pattern as the WJ seat mount holes.
I just installed some leather '03 WJ seats into my '98 XJ at the cost of $195, and that included shipping. A lot cheaper than seat covers alone for my old beat up XJ seats....
Keep in mind that the motors for the seat adjustments are located on the mounting rails of the WJ seats. So you'll loose those functions when you swap the seats over to the non-powered XJ mounting rails. Besides, how hard is it to adjust your seats manually?
The one thing I kept an eye out during my seat search, was for the manual recliner lever option, which ususally comes on the Laredo WJ model seats. I didn't want to mess with a power recliner model, and have to deal with how to make it work. Those type of seats are actually cheaper to find than the fully powered ones....