Nothing about what you're describing will be fixed by converting the rears to disc brakes. They are not proportioned enough to do as much as you're expecting. I honestly don't understand the problem you're talking about, either. You keep saying your brakes work fine, but it sounds like the opposite. Your front brakes probably need some help. Consider not just checking the material left in the pads and rotors, but also the age of the rubber lines and the age of the brake fluid. You'd do better to fully flush your fluid all around and then see if any front components are beyond wear. Replacing front rubber hoses, and even caliper assemblies, is is really easy.