Wearable sensors are a growing trend within the Internet-of- Things. Their use within many fields, such as e-Health, is more and more common and with such versatility and constraints due to their portable nature, it is important to achieve the best fine-tuning possible for the desired application. To this end, the application of the Quality-by-Design good practices of development could drastically ease the process. This study aims to apply the Quality-by-Design approach to the development of an e-monitoring solution of patient mobility. After defining the profiles of the targeted system, three critical quality attributes: autonomy, data upload duration and data integrity are defined. A criticality assessment study, based on the implementation of specific designs of experiments, is carried out to identify the most impacting process parameters. Finally, suitable operating modalities of the sampling rate, number of sensors, as well as uploading mode and period are determined to comply with the specifications on the three critical quality attributes.