My wife has winter tyres and changes them onto the original rims. This is a good solution as we bought tyre storage bags, which keep her and the car clean.
Pros - don't have to buy alloys, car looks the same, tyres get balanced twice a year, the tyre depot do all the work, tyres fitted by professionals.
Cons - have to pay twice a year to get them swapped (our deal £25 each change), risk of alloys getting damaged during change over, risk of alloys getting damaged during winter driving, can't swap immediately due to unexpected weather change.
Buying alloys+tyresPros - can buy smaller alloys and cheaper tyres, smaller tyres offer better performance on snow and ice, can change anytime, summer alloys are safe in storage.
Cons - cost of alloys, having to swap the alloys/tyres yourself, risk of damaging the alloys.
As for the tyres, have a look here -
http://www.tyrereviews.co.uk/2015 Sport Auto 19 Inch winter tyre test -
http://www.tyrereviews.co.uk/Article/2015-Sport-Auto-19-Inch-Winter-Tyre-Test.htmHad a quick look - 19 inch tyres are expensive!