To be frank, I'm not sure if replacing the single pane with double pane is: A - something I can afford at the moment and B - something I can DIY (which adds to point A)....
I don’t think shutters will provide much of an R value, but they might block out some sun. Window insulation film is a thing that exists, and might be your best budget bet. Window treatments also work well, and vary in price.
Single pane windows, would shutters be a frugal fix?
To be frank, I'm not sure if replacing the single pane with double pane is: A - something I can afford at the moment and B - something I can DIY (which adds to point A)....