I would expect any basic fan oven thermostat to fit it as long as it has the correct shaft/mounting and temperature range.
What are the names/numbers on the original stat?
As far as detailed fitting instructions go you simply won’t get them i’m afraid because of liability issues (i.e. you hurt yourself or property as a result of advice)
I’ve found a company on the internet that can supply a new stat but say that it comes as a set with the function selector as well, because this is a dual function knob and that we can’t just get the stat on it’s own?!
The two bits together are £45 including delivery ?
Your appliance is made by Nardi – you have listed a Brandt part number. The combination thermostat/switch is p/no 041099009901R, and costs rather less than £45 – an email to spares@ukwhitegoods.co.uk for prices and ordering.
You have checked that the thermostat is actually faulty?