This will help you discount a lot of options. 'Cooling only' is cheaper, but only slightly. So, even if you have another form of heating, it's worth considering a 'reverse cycle' unit as a back-up.

Obviously, the size of the room has a big influence on the capacity of the unit you need. So, take the exact measurements and note them down.

Another key consideration. A room with no insulation will require more capacity to air condition than a room with properly installed insulation.

This will affect the natural temperature of the room, and has a big influence on the type of air-conditioning required.

Knowing the size of the windows will help your choice. So, once you have the measurements of the room, measure the height and width of your windows too.