a saggy mattress的用法和样例：
- I'll go to buy a new mattress for my bed.
- With her white hairy legs poking out from her frilly pink top and rear end peeking out from a saggy pair of bikini bottoms, Angel looks an unlikely Hollywood starlet.
- There is a vein of melancholy in his character.
- There was a long lag in forwarding mail to us.