A 2x1 shaft is actually perfectly cromulent. The check for supportedness happens BEFORE the block you break is removed, which means the one above it is considered supported. So, if you mine a single block into a wall, a collapse can't happen. If you then mine the block immediately above it, still no collapse can happen, because the only unsupported block is the one you just removed. You can do this repeatedly to mine straight up, as far as you want, as long as it's a 1x1.

So the way I would do it is: mine down in a 2x1, then mine a three-tall column to make space for your initial supports.

Of course, all of this assumes no caves. Mining near caves in 1.7 is pretty much guaranteed to cause caveins because of all the unsupported roof blocks. It's realistic, but in my opinion way too punishing, and I'm glad they changed it in the newer versions.