I personally would go all out and get all 4 replaced.. you only regret it when you get into an accident.. I'm super Happy with my Goodyear Assurances, amazing in rain/snow/dry corners..
They are pricey but I picked them at Whiteoak Tire Sale for $150 each
(installed, disposed of old tires, alignment and balancing, taxes incl.)
but this sale is once a year, other than that Costco usually is a good deal, and the Costco in Brampton carries Micheline Hydroedge..
hope that helps
cheers
Martin