Working shorts (especially the dressier wool shorts I’ve been seeing a lot lately) back to a cardigan seems like a great solution. At least everytime time i see it done it usually looks really good.
For me this Summer I’m wearing a lot of shorts with super-lightweight, unlined jackets.
They work even better for me because they fit a little looser and when I am out shooting all day I have more to carry (extra battery , CF cards etc) than I can carry in a cardigan.
I have recently bought jackets from Engineered Garments, Junya Watanabe, and 45 RPM. I find I’m having an Italian Winter and a Japanese Summer.
I will have to do a separate post on these jackets soon, maybe during Pitti when I am really putting them to the test.