I would go the spring shop route as well. If you want cheap, You can find springs from Skyjacker, Superlift, Rancho ETC. They don't hold up to the weight of a actual useable truck as well though They are made for the show girl rigs, not work vehicles. A spring shop can build a set of leaf packs that will consist of multiple leafs to soften the bumps and still carry the weight of your truck/load.
I am not a big fan of rearching existing springs as they more than likely have stress points or cracks in them which will break through soon after you have them rearched. It is hard to get the temper in a spring again due to metal fatigue as well. If you put extra leafs in, make sure it is made to work with the other leafs, not just bend the existing leafs and eliminate any movement in them. Add a leafs are terrible for ride quality and do little for carrying heavy loads. If anything, they make it worse because the one Add a leaf takes the entire spring packs weight load.
Progressive spring pack sets will work good if you can get the spring shops to build them, they allow for soft ride unloaded yet are capable of heavier than stock leafs due to the overload leafs integrated into the pack. They cost more than an add a leaf, but you also get what you pay for.
Check with a localalignment shop for a reputable spring shop in your area, if the spring shop also does alignments, they usually know how to build quality springs.