Well if the front is running the standard V code springs which it likely is unless it came from the factory with the plow kit then you can go to a X code spring. Its a stiffer spring but not something that will give a bone jarring ride. It also rides better than most all aftermarket springs. You can pick up used one or new ones. I would look for low miles ones off a wrecked truck in a salvage yard.
There is really no way other than bags in the rear that are going to get you the same level ride height loaded and unloaded without also giving you a bone jarring ride with no or light loads.
Nice things with air bags in a helper role is if they do have an issue at worst you are back to stock so you are still OK you just have the standard squat if its that heavy. With anything else you are going to be stuck with big change in ride and/or difference in height.
There are some ways you could go with changing out the second stage of the dual stage springs packs but again the only way for the second stage to be triggered is from the spring pack getting flattened from the add load weight and that means the ride height is changing. Now if you do not mind riding a bit higher in the rear unloaded and then say level loaded I think that is doable. You would change out, add a, or add to the second stage bottom solid leaf which is a full length very thick bottom leaf. It has bump stops on its ends to contact the top main springs. SO once it gets to whatever height the bump stops allow contact you get a increase in spring rate. That would get you good ride unloaded and still a good ride loaded with only a certain amount of lowered ride height.