Get the light duty half ton springs since you are lowered. I asked for a set of 1/2 ton springs at the parts store, and they sold me the HD set without telling me. It leveled out my stock pickup. Made it look like a 4X4.
When I lowered it (same spindles as you) I swapped them for the standard duty Moog springs. In almost 10 years of driving it with that combo it never bottomed out. BTW, 255/70/15 tires on 8" ralleys.
Slonaker