DIY budget or renting?

You can buy inexpensive kits which stick insulation film to wooden window frames (not aluminium).

The transparent film creates a layer of still air in front of the glass that acts as insulation, just like double glazing.

You only need scissors and a hairdryer to install it. However, the view out of a window won’t be as crystalclear as plain glass, and the film needs to be replaced every 1-3 years.

More expensive DIY kits use Perspex sheets and screws but are clear 3mm plastic that’s stronger than glass.