Your experience of unnoticed coolant loss is a good reason to fit a coolant level warning lamp, which is easier than you might think:
https://www.volvoforums.org.uk/showthread.php?t=66295
This has saved my engine more than once, especially when my heater control valve snapped in half, dumping the coolant on the driveway. Having a warning lamp allows you to stop the car before major damage occours. Note the lamp to the right of the ABS lamp in the below pic.
