The Antique Sofa is a furniture item that is introduced in Nintendogs + Cats. It can be bought from Modo Home in all versions for $3,500. It can be placed in one of the four corners of your home, and pets can sleep on it.
In all three versions, it is unlocked with 1,600 Owner Points or by playing 9 days.
3DS: "Comfortable and timeworn, this sofa comes with a huge ottoman."