I don't have a car either, I only one bikes, 1 with a motor (that can carry a bike) and 3 bicycles, soon to be 4: a 70's vintage Motobecane single speed (made in france,) that is my urban cruiser/barhopper (I can afford to have it stolen). A road bike. A 9:ZERO:7 fat bike and I'm in the process of building a Salsa Bucksaw, that may very well turn out to be a quiver killer off road bike. It will have 26 x 4" wheels and a set of 27.5x3's. Last year, I put about 1500 miles on the fatty and 700 on the road, down significantly from the previous year.
one thing to consider: if you don't currently ride off road, but are accustomed to road bikes, a fat bike may or may not be the best option for you. The wheels and tires are heavy and it takes a lot of effort to spin them up. A lot. When I first got a 29er, I thought that they took a lot of effort to get going, but fat is exponentially more labor intensive. As a roadie, you may conclude that this sucks, is not worth the effort and the fattie will collect dust in the back of your garage or basement...
or, conversely, perhaps riding in the snow will open your eyes to a whole new world of adventuring by bike and you'll get into it enough that when the snow melts, you'll want to continue exploring off piste. You may also find that after a season of cranking out miles on a fatty, that your road bike now feels like a rocketship and you work in riding the fat bike as a training tool.
At any rate, to answer your question: 29x3 is no substitute for fat, but it is a good compliment. The best answer is to get a fat bike and add a set of plus wheels, 29x3 if the bike will fit 5" tires or 27.5x3 if it only fits 4" and you have a very flexible, versatile mountain bike, excellent for all seasons and conditions.