New springs for small trailer?

I have a 4x8 trailer that I use to pull my mower and stuff around every day on the wonderfully maintained streets of New Orleans, and it rides wough as hell. I have had 3500lbs in the thing and it still bounced like a wild man. Has even bounced so much that the grab handle to keep my mower running fell off. I am worried that it will stress the handle mounts on the deck and eventually crack them.

The leaf springs are all of 2ft long, and I was thinking longer leafs with one less leaf in there would ride much better. Possibly the same amount of leaves with thinner metal on them would work also. Welding new mounts on the underside of the frame wouldn't be hard.

Any comments?