If you're worried about offset voltage, get an oppamp with offset null option. I've used TLE2142 on most of my projects requiring high precision and low noise.
I don't think that would be an issue anyway. What you really need to do, is perform a 2-point calibration. Pick one temperature at the lower end - let's say 25C, and the second temperature at the higher end, let's say 220C. Run your system and record the voltage your A/D is recording at 25C, run your system again and record the voltage your A/D is recording at 220C. I am assuming your thermistor is has a linear transfer function.
Now you have two points, and once you have two points, you can plot a line, which characterizes your thermistor. In other words, if you make a plot with voltages on your x-axis, and temperatures at your y-axis, you can now convert any voltage into temperature. This is something you'd have to do anyways - to calibrate your system, and it takes care of all the other voltage drops/gains in your acquisition system.