Wheatstone bridge calculation
The resistance change of thermistors is generally big enough that you don't need a Wheatstone bridge.  Just put the thermistor in an op-amp circuit.  If you need to linearize the thermistor, that's done with an appropriately chosen series or parallel resistor -- http://www.ecircuitcenter.com/Circuits/therm_ckt1/therm_ckt1.htm