Yeah, that variation would work. You'd definitely want intrumentation amps to avoid input bias current errors. Maybe use a single voltage divider with a voltage follower amp to supply all your channels.
If you want to stick to your present amps and have the thermistor feed voltages dependent on the Vref -- bring in a -12V line, then use an inverting amp with a bit of gain to derive an appropriate negative voltage from Vref, and a non-inverting with a bit of gain to get the postive.
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