The stodgy mattress is a quest item used in the One Small Favour quest. It is obtained by talking to a man in Port Khazard, who asks the player to stuff the mattress with feathers in exchange for some iron oxide. The stodgy mattress must be taken to Rantz the Ogre in the Feldip Hills in order to obtain the feathers.
If players lose the mattress they must pay the Tindel Marchant 100 coins to reclaim it.