If you have a double-sided cylinder because there's a window next to the door, you're only mitigating the problem, not solving it. The window next to the door also means that you have a weak door frame, since the frame itself is unsupported on the window side.
If possible, get rid of the window and put something solid in its place. If you insist on natural light by the door, reinforce the frame and replace the standard glass with glass or plastic block. Its much stronger and does lend some support to the door structure.
As mentioned, for safety reasons, a latch is preferable.
Stay safe,
Mike