My choices would be as following if you plan on keeping the truck.
1. Replace 4 leaf springs with heavier 5 leaf springs. The stock 4 leaf springs are too light if you carry loads.
2. Air springs but this almost cost as much as new springs. Adjusting air pressure for varying loads is a plus but sooner or later you will have a leak. Really nice when you have a built in compressor with switches.
3. Add a leaf if springs are in good shape. Best is adding an extra leaf into the springs, do not like I would never use a half a leaf spring helper again. If the springs sre worn adding an overloader will buy you some time but sooner or latter you will end up breaking one of the old leafs.
4. Air shocks are cheap and do work but I will never use air shocks again. Springs pick up the load and the shocks are there to resist the tendency of springs to bounce and bounce.
5. Taller shackles would also work, would be the cheapest but if your springs are wearing out it will be just a matter of time before you break one.
So the first question is do you plan on keeping the truck then I would go with new springs or air springs and new shocks. If you do not plan on keeping the vehicle then taller shackles will do for now. If you look at the rear springs do they all have the same arc or or can you see varying amount of space between each leaf, this to me indicates that they are showing there age.
Cannot comment on rearcing used springs as I have never had this done. But really how long will rearced springs last if they are wearing out.
Decisions, decisions. Good Luck what ever you decide.