I consider ordering a knee long slip-on overcoat. You know, the roomy model with raglan sleeves sometimes called a balmacaan or a raglan. I have such an overcoat already, however a long model. It is not practical for driving the car or riding the bike.
These old illustrations from Das Herrenjournal and another German magazine start of 1960s give some inspiration. There was a slip-on overcoat craze back then.
A near perfect slip-on overcoat in tweed.
Herringbone slip-on with raglan sleeves and Prussian collar.
Camel hair cloth is not only for the worshiped polo coat. You may use for a slip-on as well.
Illustrations: The Journal of Style