With a thermistor or thermocouple you'd first need to know the basement air temperature, the outside basement wall surface/ground temperature and the temperature of the inside basement wall surface.
I'd crumple up tin foil around the probe end to make better thermal contact with rough surfaces.
Then it's working backward from the thermal conductivity of your wall to what it might be made of, using formulas and tables.
If the air temperature says you should be warm but you're not, the walls may cold and so you lose body heat by radiation, the other two mechanisms of heat loss being conduction and convection.
You could spend a lump sum for insulation plus labor or
pay a monthly charge for a room heater or
use a fan or furnace plenum vent to put warm house air into the basement.