What is the collective noun for mattresses?

There isn't a widely accepted collective noun specifically for mattresses.

You could use some general terms like:

* A pile of mattresses

* A stack of mattresses

* A collection of mattresses

You could also get creative and use a more descriptive term based on the context, for example:

* A nest of mattresses (if they are all together in a room)

* A bed of mattresses (if they are arranged for sleeping)

* A mountain of mattresses (if there are a large number)

Ultimately, the best collective noun will depend on the specific situation and the desired effect.