great ideathat I saw on Cults3D facebook group, I have no way to test this model so here is the link for the Fusion 360 original file:
Feel free to modify it any way , You can go back about 20 steps in the history to get the version without the cavity.
The .stls files are two version, one flat on the leg rest and one with a cavity to add some sort of cushing material (like foam or similar).
. And need a big printer or devided in parts.
The model was made from pictures