The Classic-Softie you are using is the correct model for the ECM-XM1. In extreme wind conditions, we can actually make a Windjammer to fit over the top of the Classic-Softie fur, and the details are below:
Description: 10cm Softie Windjammer
Order code: 021702
This will impact on the acoustic transparency, so a little more HF loss. But for extreme wind, it'll certainly help.
You may also find that the exposed rear of the microphone and XLR connection is a weak point at which wind noise is picked up. You could try covering it with a soft material. This we find improves things also.