An NTC sensor (Negative Temperature Coefficient) is truly analog and measures the voltage drop across a temperature sensitive resistor element. The most commonly used are "NTC 10K" and show up in tons of inexpensive temperature controllers. But even in the "10K" group there are different slope ratings (Beta curves) and to have a hope of matching an oem sensor one really needs to know the specific NTC type. It will be something like "NTC 10K B3435".
As for the "digital thermometer", it seems possible your controller can use a DS18B20 "One Wire" digital temperature sensor. These are another commonly used inexpensive digital sensing solution. I buy 3 meter wired assemblies for ~$2 delivered from ebay and I have almost two dozen of them in use monitoring my fridges, keezer, and various locations/equipment through the household.
If you can't fully identify the NTC type your controller wants you'd probably be better off going with the DS18B20 as there's only two types: "Parasitic Powered" (usually identified as DS18B20-PAR or something obviously similar) or the "non-Parasitic Powered" DS18B20. Unless a device specifically claims support for parasitic power, always go with the "regular" DS18B20...
Cheers!
