Conservatories have often been thought of as icy cold during the Winter months of the year and unbearable furnaces on the hottest days of Summer. However, that need not necessarily be the case. A discreet radiator will warm up the room in Winter but reducing the temperature at the height of Summer may be more of a problem.
Do consider having a conservatory with plenty of ventilation, including the possibility of opening roof lights. You may want to also think about about fitting blinds to shield the worst of the glaring sun from the occupants inside. Pleated blinds may not be the cheapest option available but they do look very attractive and usually come in an array of colours, including restful shades of green and cool hues of blue. Because pleated blinds have very narrow pleats, they retract neatly when they are not in use. Then when the sun is shining directly into the room, they are easily pulled down, adding a splash of background colour to your surroundings.