I think I would be interested in finding replacement springs with a PROGRESSIVE spring action. So as to avoid every freeway expansion joint feeling like you're running over railroad ties. Leaf springs are tougher to make progressive than coil springs.
On the rear, VARIABLE RATE coil spring boosters are hard to beat for a compromise between weight capacity and ride comfort. Huge shock absorbers can really stiffen the ride too much.
For minimizing leaning when rounding a curve a huge rear aftermarket SWAY BAR is hard to top.
I went to plain old-fashioned LONGER coil springs (and shocks) to cure a ride that I deemed to be "too low" on one rig. This route has its limits with steering linkage lengths.