The possessive form for the noun mattress is mattress's.
Example: The mattress's satin brocade cover looked very expensive.
The singular possessive for "mattress" is "mattress's." So if you want to talk about the mattress's comfort or the mattress's size, go ahead and do it. Just make sure you fluff those pillows while you're at it.
The possessive form of "he" is "his": He did his homework after dinner.
No, it is singular, the possessive form of it is its. The plural form of it is they or them, and the possessive form is their.To answer the question directly: there is no such word as ITS'.
The possessive form is lawyer's.
The possessive form is whistle's.
The possessive form is posse's.
The plural possessive form is Luis's.
The singular possessive form of the noun "it" is "its". Note that there is no apostrophe in the possessive form of "it". The apostrophe is only used after "it" when used as a contraction of "it is".
The singular possessive form is heart's; the plural possessive form is hearts'.
The possessive form for the noun freedom is freedom's.
The possessive form is my sister's friend.
The singular possessive form is synopsis's.