Get down right inside sofa (6)
I believe the answer is:
crouch
'get down' is the definition.
(thesaurus)
'right inside sofa' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' is an insertion indicator.
'sofa' becomes 'couch' (synonyms).
'r' going into 'couch' is 'CROUCH'.
(Other definitions for crouch that I've seen before include "Hunker down" , "Get down low" , "Squat" , "Stoop with knees bent" , "shooter?" .)