The widespread use of computers in work and academic environments has increased the risk of health issues due to poor posture, such as cervical and lumbar pain. An approach to mitigate these risks is to incorporate body monitoring systems that provide feedback on the user’s posture. This study presents a posture monitoring system that uses a sensorized chair equipped with load cells to detect body weight distribution on the seat and backrest, along with a headband with inertial sensors to measure angle. A computer software records these signals wirelessly and notifies the user of any incorrect posture. The weight sensing feature was characterized in terms of sensitivity, offset, and repeatability. An experimental evaluation was conducted involving 15 participants, each undergoing a 20-min posture monitoring session while performing office tasks, followed by a questionnaire assessing system usability and the relevance of posture alerts. The results indicated a sensitivity of the weight sensors close to 1 kg/kg, with low variability across repeated measurements. Performance scores exceeded 4.7/5 in accuracy, ease of use, and real-world implementation potential. The prototype effectively detected and monitored seated posture, sending alerts when incorrect positions were adopted. Future work will focus on miniaturizing sensing components to meet comfort requirements, incorporating artificial intelligence algorithms to enhance real-time posture classification and alert generation, and conducting long-term evaluations in office settings.