Willism the zone thing in the US is just as bad. I am zone 6 according to the map. But I. have the same problem you described.
Our rainy season starts in September. Just when the ground is water logged the rain changes to freezing rain which changes to snow. I end up with bock of ice around the plant roots.
For this problem I use gravel. The cactus are over gravel with a sprinkle of soul. That is 90 percent gravel 10 percent soil
