Yeah it will be quite an initial outlay to get another set of wheels + tyres but might be the best route - I have run flat tyres so cross climate options are limited there too.
We've dome some ropey drives home from the highlands in snow last year and only just made it back - so many others had come off the roads. We're on the edge of Loch Lomond national park and commute into Glasgow - the roads are not what I'd call major until we get close to Milngavie/Bearsden so I do expect snow/ice to be a problem.
I'll head to ebay and see what wheels are around for my e90. Cheers