© 2021 IEEE.The emergence of WBANs with health monitoring capabilities has greatly revolutionized health care. Enabling WBAN nodes to be fully autonomous is critical in making this thrust sustainable. However, regular charging of batteries in such systems remains a significant inhibitive factor. In this work, Health Monitoring Energy System (HeMeS) tool previously developed by our group using comprehensive analytical models is utilized to study various energy flow scenarios in a particular health monitoring WBAN node powered by a hybrid thermal-vibrational energy harvester. The use of HeMeS for design space exploration is thus demonstrated for various patient categories, incorporating environmental factors, electronic load activity levels, and system cost/size constraints. The described comprehensive system design approach of incorporating transducer, electronics, user environment and data duty-cycling profiles, is demonstrated to be viable and appealing for delivering sustainable WBANs that directly contribute to climate-neutral society without significantly increasing cost.