New drywall against existing walls
 

Had a similar situation with my folk's house in 1995. We moved the door
from a bedroom closet to the hallway. I put in studs and drywall in the
old opening. For some odd reason that bedroom ( the smallest of the
three, also my old room) had two closets--one on either side of the
room. We did the modification to use that closet for the central air I
put in. Anyway,my mother (then 65y/o) taped. floated, textured and
painted it, and you couldn't tell by looking at it that it wasn't that
way since the house was built. I live about 250 miles away and had to
get back home after finishing the a/c install, so I wasn't there when
she did it. I don't know how long it took or exactly how she did it,
but the average pro probably wouldn't have done as good a job. Larry