There might be a way to get temperature without a microcontroller at all. IIRC these RF modules are OOK (on off keyed) so any square wave will go thru. You could use a CMOS 555 timer and make an audio oscillator using a thermistor.
Transmit that, and receive it into a digital pin on the other end.
The receiving Arduino can determine the frequency of the square wave, and convert to temperature. Either a polynomial equation with a couple of calibration constants or else a lookup table and interpolation would work.
Not that your approach is bad either, nice work!