Bottom smacks warming couple at night? (3,5)

I believe the answer is:

bed socks

I'm a little stuck... Click here to teach me more about this clue!

'bottom smacks warming' is the definition.
I know nothing about this answer so I can't tell whether this works.

'couple at night?' is the wordplay.
'couple' becomes 'bed' (bedding is a kind of coupling).
'at night?' becomes 'socks' (I can't explain this - if you can you should give a lot more credence to this answer).
'bed'+'socks'='BED SOCKS'

Can you help me to learn more?

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app