I admit it. I was wrong. And so I take back what I said about the unsuitability of the cotton suit. It does have a place, even though the economics remain a bit questionable (cotton has the same tailoring cost as wool and a much shorter life). In an eight ounce weight with 10-15% cashmere it is smooth, lightweight and warmer wearing than I had ever expected, making it a nice choice for casual shoulder season days with temperatures in the 60s (perhaps 18 degrees C).
Eight ounce cloth is something I eschew in wool as it wrinkles easily without being particularly cool. But in cotton, a few wrinkles are part of the character. They help a suit to fit in when it is worn in the suburbs, for example, where suits are rare. And cotton does not seem inclined to any more of them than wool of the same weight.
Try it in tan, navy, olive or dark brown. Gray would be a step too far.
In the photo, Matteo Marzotto in dark brown cotton.