A thermistor is far from linear. I would not use it now, at least without first trying other things.

I came up with a simpler solution to your problem. Drop the op-amp and drive the LM35 output to one ADC of your PIC. Now drive the raised GND of the LM35 to another ADC input of your PIC.

Since the two voltages, referenced to ground, are positive, you can do a calculation in your program. (LM35output-LM35Gnd)*100 and you will have your temp. Be careful here because the subtraction will give you a negative result if the real temp is below zero.

So now you have a circuit absolutely minimal.

I would suggest to use a PIC with 10bits ADC and increase the resolution with oversampling to 12 bits with Darrel Taylor's oversampling routines when you have it working.

Ioannis