If your source and load have a common ground, you can use a simple resistor voltage divider. If you are concerned of temperature variation, you should work on the divider, select stable resistors or use a thermistor, and calibrate the divider over temperature.
Without the common ground you will have to use a capacitor voltage divider, and again calibrate its response over temperature, etc. You can also use an audio transformer (like in old phone modems), the same procedure.