The plural is MATTRESSES. See dictionary.com http://dictionary.reference.com/search?q=Mattresses
The singular possessive form is heart's; the plural possessive form is hearts'.
The plural of rose is roses. The plural possessive is roses'.
The plural possessive is governesses'.
Possessive for sofa is sofa's. Plural for sofa is sofas. Plural possessive is sofas'.
The plural is queens. The plural possessive is queens'.
Singular possessive: secretary's Plural: secretaries Plural possessive: secretaries'
The plural is lads. The plural possessive is lads'.
The plural is relatives. The plural possessive is relatives'.
The plural form is suffixes. The plural possessive is suffixes'.
The plural form is stepsisters. The plural possessive is stepsisters'.
The plural form is Mexicans. The plural possessive is Mexicans'.
The plural form is echoes. The plural possessive is echoes'.
The plural form is inches. The plural possessive is inches'.
The possessive form for the noun mattress is mattress's.Example: The mattress's satin brocade cover looked very expensive.
Studies' is the plural possessive of study.
The plural possessive is pals'.
Coaster's is singular possessive. The plural is coasters, the plural possessive is coasters'.