have you tried thermilate insulating paint additive, it helps keep heat in the room(works by reflecting the heat back in the room).
from FAQ on thermilate website
"Q. Can Thermilate be used on conservatories?
A. Yes it can. Thermilate can be applied to a varnish or lacquer, that can be applied to the inside or outside of the conservatory roof. It will make the glass go opaque, not totally clear. The colour will be an off white as Thermilate is not clear. "
you can find out more at
Insulating Paint Additive, Insulating Paint, Eco Paint Insulation, Energy Saving Paint
