1998 Toyota 4Runner 4WD LTD Shock Upgrade Questions

I have a 1998 toyota 4runner and I would like to replace my shocks, I have heard that air shocks make the ride alot smoother on and off road.
My current stock shocks are very stiff and I feel every little bump in the road. Does anybody have any recommendations, I wouldn't mind an inch or two of a life eather. How much are we talking here???

Thanks
ruvt4runner98