Thermistors are a simple but very precise method of measuring temperature. The resistance changes dramatically as the body gets colder and hotter. Thermistors tend not to be used for very hot temperatures (these low cost ones have vinyl wires that top out at 100c degrees C) but they’re much cheaper than thermocouples and very easy to read using a simple voltage divider. They’re more precise than digital temperature sensors (those always have an error of +-1 degree C) at 1% you can get better than +-0.2 degree C. These are often used for cold/warm temperature sensing and for battery chargers.
We carry a basic 10K 1% NTC thermistor but you can also pick up a range at digikey.