Sort of underwear, if cold in bed (4)
I believe the answer is:
lacy
'sort of underwear' is the definition.
'cold in bed' is the wordplay.
'cold' becomes 'c' (eg on taps).
'in' indicates putting letters inside.
'bed' becomes 'lay' (I've seen this before**).
'c' going into 'lay' is 'LACY'.
'if' acts as a link.
(Other definitions for lacy that I've seen before include "Fine" , "Resembling open fabric" .)