If you go fatter on the rear tires, it's best to match both front and rear tire sizes.
195/60R15 rear matched to 175/65R15 front gives you an extra 10mm front and rear tire width plus 6mm extra sidewall height on the rear tires and 6.5mm extra sidewall height on the front tires. Or put another way, the outside diameter of the rear tires increases by 12mm and the outside diameter of the front tires increases by 13mm. So as well as an extra 10mm in tire width you increase the outside diameters of the tires by about 0.5". It all adds up to that bigger look.
Vredestein Quatrac 5 195/60R15 88H

Vredestein Quatrac 5 Tires
Find Vredestein Quatrac 5 tires at great prices, customer reviews and more from the Internet Source for Vredestein Tires, Vulcan Tire Sales (vulcantire.com). Fast shipping to your home or installer.
www.vulcantire.com
Vredestein Quatrac 5 175/65R15 84H

Vredestein Quatrac 5 Tires
Find Vredestein Quatrac 5 tires at great prices, customer reviews and more from the Internet Source for Vredestein Tires, Vulcan Tire Sales (vulcantire.com). Fast shipping to your home or installer.
www.vulcantire.com
The benefit of going for these two tire sizes is that they are both common tire sizes so you shouldn't have too much difficulty finding other matching front and rear tires in these sizes when replacement time comes.
Other matching sizes include 195/55R15 rear and 175/60R15 front. However, you might not be able to find good quality matching tires in the North America market. There's a little more availability in Europe for these sizes, so it's an option there.
Here's some winter tires in 195/60R15 and 175/65R15 sizes:
Continental VikingContact 7 195/60R15 92T XL
Continental VikingContact 7 175/65R15 88T XL