Like you, we used thin plywood. The plywood bends easier in one direction. You want the easy bend in the up-down direction. The panel doesn't need to bend front-back.
Of course, we got it wrong so I cut horizontal groves in the back of the plywood to make it more flexible. Cut it about 1/2 way through.
There was some recent posts about this subject. One guy used aluminum and it worked our really well.
I have a pix what it looked like installed. Since the picture was taken, I have installed arm rests which help to draw the bump in the lower edge in.
