Your old habits know your weak moments. Plan for those, not your strong ones.

Plans get made on good days by a rested version of you who cannot imagine failing. The habit you are trying to break does not appear then, but at eleven at night, after a bad shift, when you are alone and tired. Designing for your best hours is why most plans collapse in the ordinary ones. The plan has to survive the version of you that is worn out.

Name the two situations where you always slip and write them down specifically. Decide now what you will do in exactly those moments, down to the first action. Make the fallback so small that a tired person could manage it.