Wearable sweat sensors are rapidly emerging for continuous and noninvasive monitoring of ‘wet’ parameters not included in current commercial wearables. This paper investigates the optimization of screen printed sweat sensors, intended to ultimately be compatible with large scale, roll-to-roll, fabrication. Sweat sensors containing Na+, K+ ion selective electrodes and pH sensing elements were screen printed on polyethylene naphthalate films with different electrode array designs. For sensing Na+ ions, a PEDOT:PSS transducer layer was found to effectively improve the sensor performance, showing an up to 32% sensitivity enhancement of up to 113.3mV/decade. Large working electrode sensing area was found to play an important role in achieving high electrical sensitivity, and the position of the electrodes influenced the individual sensor performance. These findings provide a solid foundation for an optimized development on wearable sweat sensors.