webcou,
Firstly, welcome to the forum. It's a good, if slightly crazy at times, place to be.
Secondly, definitely get a dedicated set of rims.
Thirdly, going down a size, at least in terms of width, might afford you a better grip. You can indeed save money by dropping a size in terms of radius but it might raise other questions. I'll have to bow to the tire gurus here. If you are not at all sure about quality of the lesser known brands, stick with the main brands (Yokohama, Michelin, Toyo, Bridgestone (Blizzak)). I don't think you can go wrong with those. The shop you finally pick will help you there.
Speaking of shops, I use Alignements Desjardins on de Maisonneuve Blvd. West. They are quite good but they are only one of several in the area (NDG, either on de Maisonneuve or St. Jacques).
Hope this helps!