For the skin, just about any sensor would work. For better contact it may mean having a small low thermal resitance disc or such like to increase the surface area, to which the sensor is attached. The list of sensors is extensive, thermistor, diode, Integrated circuit, thermocouple etc. Most will require some sort of electronics interface, allowing the signal to be converted to something that can be read by a human, and some will require calibration. From that perspective, some of the temperature sensing IC's are most useful, many could be connected to an arduino, microbit, or some similar system, with a bit of code they can display the temperature in degrees.Cheers,Richard
