How about coil spring kits? I have a pair on mine, work well enough for the prices. It won't give you increased load capacity with bad leaf springs, but my leaf springs are flat and this helps the ride a lot, lifted it 2".
https://www.autozone.com/suspension-steering-tire-and-wheel/leaf-spring-assist-kit/superior-automotive-leaf-spring-assist-kit/975039_0_0