If you do not want a rough ride, then keeping to a near OE spring rate will help ... Somthing like the HPF, H&R OE Sport would be good choices. The nice thing about the HPF is that it is a kit of shocks and springs ...
Springs alone, are only 1/2 the equation in a suspension setup that works right ... Shocks are as important or more important to ride quality than springs. (Lets not get into bushing, sway bars etc and how they impact ride quality)
Most aftermarket (higher rate springs) will not be matched to the valving in the OE shocks. this mis-match in valving will do a couple of things, wear out your OE shocks faster, and will probably not have enough/proper valving to completely damp the springs. This will cause in many cases a "bouncy" ride.
It is reccomended to optimise both ride quality and suspension performace by matching your springs with appropriately valved shocks. You get appropriate shocks, by either buying them as matched set from the manufacturer, or by purchasing a shock with variable valving ie Adjustable. An Adjustable shock will allow you to match the valving to the spring, and optimise the performance.
Moose