1965 c20 suspension questions.

[Green chevy c20]

Hi how its going. I have a 1965 chevy c20 truck. This truck has the stock suspension with the coils up front and coil with the left springs in the back. When you drive this truck on a straight road it drives very nice,but as soon as you hit some bumps the truck is very bouncy.I think it is due to the stiff springs in the rear. I have kyb gas ajust in the shocks in the front in rear. I just want to try to get a little better ride as i am going down the street as it is my daily driver. I think i have about 500 dollars max to spend. Just wanted to see what you guys think. i heard from a friend of mine that you could maybe put c10 springs in the rear. or i was looking at some dual rates springs but not sure about them. The only thing i will ever tow is a small boat so i dont need a stiff rear suspension. I was also thinking to leave the front alone and get softer springs for the rear and hopefully it will drive better. Thanks for any advice.