Consider using this yellow 8x2 character OLED to replace your existing STN character display. OLED character displays are great if you're building a low-power device as they require very low amps, only 16mA for this OLED display.
8-bit or 4-bit parallel interface.
The WS0010 controller interface is very similar to industry standard Hitachi HD44780.
Under OLED Modules: Parallel Character OLED 8x2, RoHS Compliant, Yellow, -40°C to +80°C