Summer's here and the conservatory regularly tops 100 degrees even on
overcast days.

What are the best ways to keep the temperature within sensible limits
?

I've seen adverts for thermal inserts that are slid into the
polycarbonate roofing. The lack of any pricing structure leads me to
suspect that it's not cheap and will be a high-pressure sale of a
largely ineffective product. Is it worth considering ?

Other obvious solutions might be to use a thermostatically controlled
extracor fan or some sort of shading in the roof.

Has anybody any suggestions or observations ?

It's only a small conservatory, less than 3 metres square and south
facing.