Behaviour change, crucial in health interventions, demands an understanding of the end user’s psychological, social, and environ- mental contexts, often overlooked in user modelling. This paper advocates integrating behaviour change theories into user models to improve personalisation based on individual characteristics. We introduce a novel, enriched with psychological theories, framework for using dynamic user Personas within Digital Behaviour Change Interventions, allowing adaptation to evolving user behaviours and preferences. The dynamic user Personas offer a detailed rep- resentation that accounts for the complex stages of behavioural change and COM-B patterns. We also explore the transition in user modelling from expert-driven to data-driven methods, highlighting the importance of acknowledging both interpersonal and intraper- sonal variations in user behaviours. Our proposed semi-automated system model merges these modelling methods, enhancing person- alisation in health interventions by addressing human behavioural complexities. Additionally, we discuss the ethical and privacy is- sues involved, ensuring responsible and secure data management. In conclusion, our approach conceptually links behaviour change, interaction design, and user modelling, setting a foundation for further empirical research and digital health applications.