I'm making grommet top draperies with blackout lining as a surprise housewarming gift for my daughter. Her City sofa is placed beneath her living room window in her small 1954-era home. I want to make "stops" to keep the sofa from sliding on the wood floor and "smushing" the draperies when someone sits down.

Assuming a right triangle behind the sofa formed from the feet, the tilt angle of the back and the vertical height from the top back to the floor, what is the length of the base of the triangle? The width of the rear legs will also be helpful so I can make a "U" bracket in the stop to cradle the legs. I need the Forum's help because I'm in NC and she's in VA.

Your help will be greatly appreciated.