Shocks absorb impact from sudden jars and allow the axle to travel up/down quickly. The coils are what actually supports the weight of the vehicle though. Over time both shocks and coils loose their ability to rebound as firmly, making the ride rough where you feel every bump (bad shocks) and bouncy (bad coils).
Usually you replace all components. If your coils are no good and you put brand new shocks, they are going to take a beating and fail much sooner than they should. Plus a shot suspension will ruin your tires quick.
If you want a stock ride, why not replace with stock parts? It's $170 for both coils from Toyota of Dallas and only $60 for both shocks for a brand new Toyota rear suspension. The front is significantly more expensive though.
Toyota Parts and Accessories - Genuine OEM at Wholesales Prices | Toyota of Dallas