You planning to keep the spacers with the new springs? Then you need shocks for the proper travel with that setup.
If you plan to remove the stock coils and spacer and replace them with the new springs, then I'd suggest you contact the lift mft for suggested proper length shocks for the lift.
However, if you go from stock and 2" spacer lift to a 3" spring lift, is that cost effective to go bigger? Add a small 1" body lift, trim the front fender for flat fender look, and raise the rear flare. This will provide greater room for larger tires, provide the option to lift the engine for better vibe control with a lifted Jeep, provide opportunity for adding a flat belly pan/SYE for better belly clearance.
