Best way to package graphics cards?

So l'm selling a used 3070. I have the original box, and put the GPU in an anti static bag before repackaging it.

The original box measures 38L x 21.5W x 10D cm.

I'm wondering what size box I should get to put the original box in, and what kind of cushioning I should use and how?

I don't know where to get boxes, so l'm just ordering some on Amazon. Ordering a box within a box to put a box in.