Whatever is used should have a sufficient specified breaking strain and be static (i.e., not stretch).
The width of the ligature matters. Contrary to popular belief, wider isn't more comfortable. Yes, it may be more comfortable on the skin initially, but the inability to close the arteries quickly makes it uncomfortable with the extreme head bloating. The preferred thickness is finger size or smaller. If you still want to use a belt, you can't tie the belt in knots to the doorknob, but you wedge the other end in the door jamb and close the door, as shown
here