Sedentary behavior and spinal health issues are caused by poor postures. It has become a global public health challenge. This paper integrates to the Fogg Behavior Model (FBM) with spinal biomechanical monitoring technology to explore and design a health digital product service system. It aims to correct and remind users of their sitting postures and enable them to use it continuously, thus ultimately improving their spinal health status. In the first phase, this study proposes a multimodal wearable system that integrates flexible sensing, augmented reality (AR), and gamification design to achieve full-cycle spinal health management. At the hardware level, the system employs a four-node distributed flexible sensor patch network, covering key regions including the cervical, thoracic, lumbar, and sacral vertebrae. The software layer constructs a dynamic 3D spinal model with 24 degrees of freedom and combines AR camera-based recognition. In the second phase, this study recruited 6 long-term sedentary participants to evaluate the designed spinal health system. The objective of the SUS test is to measure users’ satisfaction towards this system. Then, the open-ended interview aims to comprehensively understand the root causes of its challenges and strengths. Therefore, through multimodal data fusion and immersive interaction design, this study establishes a new paradigm for spinal health management in home settings.