The comfort of a smartwatch is recognized as a pivotal determinant affecting users’ engagement with the device. This study delved into the intricate interplay between smartwatch comfort, users’ behavioral intention, and their actual usage behavior within the specific context of sleep. Through the lens of a structural equation model, we find that the appearance and movement dimensions of comfort significantly influence users’ intention to wear the smartwatch during sleep, while other dimensions like pressure, harm, attachment, and perceived change do not show significant effects. Furthermore, this intention significantly translated into smartwatch usage behavior. Building on these insights, we subsequently embarked on an exploration of how personality traits interplay with comfort and intention to impact smartwatch usage during sleep. The moderated mediation models revealed that the personality trait of openness acts as a moderator, amplifying the relationship between smartwatch comfort and behavioral intention. Individuals with higher levels of openness exhibit increased inclination to adopt the smartwatch during sleep, even when comfort is compromised. These insights contribute to a nuanced understanding of smartwatch usage behavior and offer guidance for personalized design strategies, especially within the sleep context.