The most common and most likely answer to this crossword clue is the 6 letter word AIRBED
A
I
R
B
E
D
Buddy explains!
The straight part
We know that "mattress" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mattress = airbed.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AIRBED mean?
AIRBED noun- A bed that is inflated with air and used as a permanent or temporary bed. They are adjustable, and sometimes portable.