Can you specify the temperature accuracy you need over what range?
I achieved a 0.1 degree Celsius resolution with a 10 bit ADC from -20 to +120 degrees Celsius by only adding a transistor and a second resistor load for the thermosistor so when the light load on the thermosistor read too low a value on the ADC, I turned on the transistor, just like changing the range the range on an auto ranging ohm meter, to get that extra precision at lower temperatures.
Well, combined with oversampling, you now can get 0.025 degree precision. I think your thermosistor wouldn't be that precise anyways..