There are four shock absorbers on your car. The rear ones are air shocks, and the front are conventional shocks. The air shocks can be troublesome; there is a conversion kit available to replace the air shocks with conventional shocks. If you do this; all four shocks will be replaced. But if you are happy with the replacement air shocks you now have; than just replace the front shocks.
There are three grades of shocks available for this car; I strongly recommend buying KYB Gas-A-Just gas shocks; as they are less expensive than many other brands, have a lifetime warranty, and give much better ride and handling than other brands of either gas shocks or non gas shock designs.