I don't want to use a voltage divider with resistors, because I lose precision.
Yes, resistor divider, an ADC with more than 10 bits of resolution and a precision voltagereference would do better than a difference circuit
I think this might be the way to do it properly (please correct me if I'm wrong).Find the center voltage between 9v and 14v >> 11.5volt.Calculate the input voltage divider so that 11.5volt on the input gives half of the opamp's rail voltage (2.5volt).e.g. 18k/5k.Pick equal values for R3 and R4.e.g. 2x4k7The opamp's output, with 11.5volt input, will now be mid-voltage (2.5volt). Independent of the value of R5.R5 gives the required deviation of 9-14volt by changing the virtual ground (-input).~8k2 should do it.