We’ve had this bed 3 months for our dog, he’s 30kg, so not overly heavy. 
The sides have all collapsed out of shape, I would expect that if he was using the walls of the bed as part of where he lies but he doesn’t, he curls in a ball on the mattress. The walls are reshaped everyday but they are just wadding which is slowly losing its shape. 
The memory foam mattress is just a thin topper (approx 1.5-2cm thick) on top of wadding too, not the quality I would have expected from SilentNight.
Not the bed we expected it to be, disappointed.