The transition to smart factories is a critical challenge within modern manufacturing, characterised by the need to integrate advanced digital technologies with traditional production systems. Existing approaches often fail to address the complexity of such integration, resulting in inefficiencies and missed opportunities for innovation. This paper presents a structured, three-phase model to help companies digitally transform their manufacturing processes. The first phase focuses on the benefits of integrative planning, identifying planning process challenges and assessing readiness for digital planning using aids such as Success Stories and Quick Checks. The second phase looks at planning domain selection, covering the necessary planning processes, interfaces and information flow, supported by detailed process profiles and a reference architecture. The third phase explores digital factory planning methodologies, examining process optimisation opportunities and the application of AI, facilitated by a potential catalogue Together, these phases enable companies to reap the benefits of Smart Factories, overcome planning challenges and improve their digital planning readiness, providing a holistic approach to the digital and integrative development of production systems.