Supported decision-making (SDM) is a principle guiding mental health service provision, which aims to improve people's ability to make informed decisions about their care. Understanding diverse individual needs is vital to its success. Based on 29 narrative interviews with people diagnosed with mental illness in Australia, we examine how participants reflected on their own experiences of SDM. We find that participants' conceptualization of mental health expertise, their own experiences and sense of agency, and their varying needs for dependence and independence influenced their relationships with mental health practitioners. These factors in turn shaped their expectations about SDM. Four narrative positions emerged: the "Inward Expert," the "Outward Entrustor," the "Self-Aware Observer," and the "Social Integrator." These positionings influenced the type or style of support that participants expected and considered most useful. Our findings are relevant to developing effective approaches to SDM that take into account service users' needs and preferences.