Considerable progress has been made in developing sensors and wearable systems for monitoring physiological parameters in different fields. Among all, healthcare and sports are showing increasing interest in monitoring respiratory rate through these sensors. However, several open challenges limit their reliability. This study presents the design, development, and testing of a wearable sensor based on conductive textiles for respiratory monitoring in sports. Our approach involved an initial analysis of the breathing kinematics to investigate the magnitude of chest wall strains during breathing. This analysis was useful to guide the design of the sensing element, as well as the metrological characterization of the sensor and its integration into a wearable strap. A pilot experiment was then carried out on a healthy volunteer to assess the sensor's performance under three different breathing patterns (bradypnea, quiet breathing, and tachypnea) using a wearable reference system. The obtained results are very promising and aim to contribute to developing a reliable and efficient wearable device for monitoring respiratory rate. Furthermore, the design process employed in this study provides insight into the attributes needed to accurately capture breathing movements while maintaining comfort and usability.