Grill working but oven won't heat up, fan working ok. Is it fixable and how difficult would it be to carry out myself?

The only thing left sounds like the thermostat. Several online appliance parts stores are very helpful.

sounds like the control switch to me. if you have already taken it apart it's the switch with the most wiring.

its possible that your element has blown

it has to be the temperature control itself...thats the only other component, aside from the high-heat cut out switch which rarely goes bad.

If the fan is working o/k, then there is little doubt that the oven element has failed.
This is quite common with fan assisted ovens.
The element is usually located at the rear of the oven compartment behind a removeable cover.

Oven functions
Oven light.
Upper and lower heating elements.
(Conventional cooking).
Upper and lower heating elements with fan.
(Fan assisted cooking).
Lower heating element with fan.
Inner grill heating element.
(Radiant grill).
Full grill heating element with fan.
(Fan grill)
Rear circular heating element with fan.
(Fan forced cooking).
http://www.sampfordixl.com.au/lagermania/specs/f969d5x.pdf

possibility is that the wire that link the oven element and that of grill is loose or burnt