The most common and most likely answer to this crossword clue is the 8 letter word MATTRESS
I've seen this crossword clue in The Daily Telegraph
M
A
T
T
R
E
S
S
More clues leading to the result MATTRESS
- Mess tart about in bed
- Large pad of hair behind back-to-front cap
- Tart crumbled in officers’ dining room makes a soft base
- Lover one’s abandoned for a time? Sleep on it!
- Mother takes time with hair – one probably in bedroom?
- Place to sleep has floor covering and lock
- Nap on this rug upsetting 6’s
- Dull tension, topless in bed
- Mother, tense, rests somehow — on this?
- Hat put over hair one’s slept on?
Buddy explains!

The straight part
We know that "Nap on this rug" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nap on this rug = mattress.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 MATTRESS mean?
MATTRESS noun- A pad on which a person can recline and sleep, usually having an inner section of coiled springs covered with foam or other cushioning material then enclosed with cloth fabric.
- A form of retaining wall used to support foundations or an embankment
- To cover with a thick layer, like a mattress; to blanket.