Someone posted a list similar to this that I adapted to me. So, here is what I do...

As soon as it dips below 15°C I add knee warmers;

Between 13°C and 15°C, I add a sleeveless or short-sleeved base layer and long finger gloves;

Between 10°C and 12°C, I add arm warmers and long merino wool socks;

Below 10°C I swap out the short-sleeved jersey for a long-sleeved jersey, light balaclava;

Below 7°C I swap out the knee warmers for leg warmers, and add a wind vest, shoe covers;

Somewhere between 3°C and 0°C I swap out the vest for a jacket, fleece balaclava, winter gloves