DYI Blanik L-13 cushion

All,

Having sat on the famous steel bar for much too long, I decided to
make a seat cushion for the front cockpit of our club Blanik L-13.

I am planning to use plywood as a base and 1'' CONFOR foam at the top
layer.
At the lowest point, the foam will be glued directly to the plywood.
In the front and in the back, I am going to need some sort of a
filler. So far, I have considered the following:
- Wood. Firm, will not compress, heavy, cheap. Difficult to shape.
- Balsa wood. Firm, will not compress too much, light, not so cheap.
Easier to shape.
- Foam. Fairly firm, 3'' block of it compresses less than 0.5'' with
200lb of me standing on top of it, light, free. Easy to shape.

You might guess that I would prefer to use foam. But then, I have read
a lot about the dangers of sitting on _any_ foam that is not "energy
absorbing."

Any advice/ideas? Oh, and does anyone have drawings or photographs of
a factory-made Blanik cushion? I have not yet decided on an exact
shape and I would rather not reinvent the wheel.

Thanks!
Bart