They are two different lines....not that they haven't been confused or changed over time.
Crouch is an Anglo-Saxon name and derives from someone who lived by a cross.
Couch has two different origins. It is a Cornish name thought to have derived from Cornish "cough" (red) and to have been a nickname for a redheaded man. There is also an English name Couch which probably originated as a name for a maker of beds or bedding