any1 got any idea how easy/difficult it is to change the door on the octavia? Or is it best left to a bodyshop?

I would have thought that it shouldn't be too bad. Take basic precautions of taping over any adjacent paintwork in case of slips causing scratches. I think that there may be bolts close to the actual pivot of the hings, undo these and the door will come off. An assistant and a trolley jack with a bit of wood on it would be invaluable. The wiring will disconnect from within the footwell panel