### Clue: Used to beat mattress after changing the cover (6)
### Answer: MALLET 
 ### Explanation: Definition: Used to beat
 "pallet"(a straw-filled mattress – not very comfortable, I'd say) **with its first letter replaced by** "m"(after changing the cover).
Answer: A short-handled hammer with which to beat or drive in a chisel, wedge, etc.