You have not mentioned the relay solenoid current.
I would be wary of using a resistor in series with a freewheeling diode across a relay solenoid because the current spike is high and could produce a high voltage spike across the resistor which would defeat the purpose of the diode. A zener diode in series with a regular diode would be better because it would only conduct the highest voltage spikes and the relay would function better (a plain diode across relay coils is bad for the relay switch contacts, according to this short article:
Coil Suppression Can Reduce Relay Life).
The zener diode needs to have a voltage rating between the supply voltage and the MOSFET's maximum Vds rating so that the spike never goes above it. For example, if the supply voltage is 24V and the Vds(max) is 60V, the zener voltage should be between 30V and 40V. The power supply voltage should not be reaching the zener voltage (if you have an unregulated power source).
The zener diode should have the highest power rating you can get. 0.5W and 1W will not be enough. You could also use more than one zener and share the voltage drop (as well as the power) across them equally, and then you could use lower power zeners.