[2] In promotion of the album, the band also released their debut single, "Magic Forest",[3][4] which reached number 11 in the Netherlands.

[5] Fat Mattress was later reissued in 1992 by Sequel Records featuring five new songs, all of which were later included on the 2000 compilation album The Black Sheep of the Family: The Anthology (which also contained three more previously unreleased songs);[2] Castle Communications subsequently re-released the 15-track reissue on 5 March 1996 under the title One.

[6] The album was reissued again on 29 June 2009 by Esoteric Recordings with eight bonus tracks, all of which had already appeared on The Black Sheep of the Family anthology.

[9] The album was described, in a review for allmusic, by critic Richie Unterberger as "passable, pleasant late-'60s psychedelia with a far lighter touch than the hard bluesy psychedelic rock Redding played with Hendrix.

"[2] Unterberger went on to suggest that the album is "often like an amalgam of the Byrds, Buffalo Springfield, Moby Grape, and Love, with some passing nods to British psychedelia by Traffic [...], the Move, and the Small Faces; there's even a bit of a Monkees-go-spacy feel to 'I Don't Mind.