If they still sell shocks with spring assist that would be my first choice. Ditto air shocks--Replacing springs on a car that old is a job for a spring shop and would not be cheap. I speak from experience.
Actually, replacing the rear leaf springs is not rocket science and anyone with the slightest amount of mechanical know-how can do it. The problem lies in the fact that 9 times out of 10 either one or both of the front bolts will be rusted and frozen so it can't just be taken out like a regular bolt. The bolt has to be cut out. I used a recip saw, and others have used cutting torches to air grinders. But, at any rate, be prepared to have to cut out the bolt.