Or add two more leaves to your existing pack... I took an XJ main and second leaf and added them to my pack...
I cut the eyes off the mains and put the leaves in the pack and made some unique clamps to allow it to droop but control body roll.
Since I'm on 1 tons I captured 3 leaves with my clamp at the back... for you probably 2(the two mains) would be better for flex and just as strong.
By adding the two springs, it helped to gain a small amount of arch back, and it also adds some load carrying capacity. Depending on how you clamp them together, it will droop just as well as before or better or worse... whatever you want. I clamped the hell out of my leaves because I've got a locker and could care less if I lift a wheel... it's dead stable and feels great.
Here is the way I clamped the packs at the back:
I don't have an official "before" picture, but here is one where you can see how badly it was sagging a week or two before I fixed it:
This was where it sat AFTER adding the two extra leaves:
I was in the same boat as you(springs S shaped and sagging), and think this will work for quite a while.
All you really need are some 5/16 allen head bolts(and nuts) to replace your center pin, and some kind of clamps to replace the old ones. If you're careful, you could try reusing them, or you can go to a spring shop and get the hammer-on style clamps that I used. The "kit" for spring clamps that I got was from Autozone... you'll need either 2 kits(for the extra plates), or some 3/16" plate to make your own.... Basically I welded the lower plate to the U-bolt looking piece... then the other one gets sandwiched with nuts around the top leaf.
Here are the hammer-on style clamps I used... I put one each on the other side of the packs(my ghetto homemade clamp at the back, hammer on at the front).
Those are stupid cheap... should be no more than like $6 each.
Note, on my TJ the XJ leaves are swapped around backwards, so the long side is the front and the short side is the back when I refer to them up there.