Anyway just in case more tips below

1. Created obj in Wings - remeber prop must have "open bottom".

2. Under prop I placed windforces which hold mattress in correct shape.

First clip with jumping boy was created with 6 windforces, second with woman sitting on bed with 15. I set amplitude 0,5 and angle 50, range 0,5 turbulence 0. 
I recommend place windforces first in rows and collumns and later translating prop along Y axis till dynamic calculation gives correct results. Then Parent all forces to mattress prop (now can be translated together.