The determining factor in "bend-ability" of strings is tension. The lower the tension, the easier it is to bend the string. It doesn't matter how thick the string is....if the tension is low, it'll be easy to bend.
If you take a .012 string and tune it to E on a full 25.5" scale guitar, you'll have 23.32 lbs of tension as opposed to 12.28 for a .009 string. That's almost twice the tension, and I think that qualifies as hard to bend. Unless you have finger muscles like a gorilla, it's going to slow you down and limit how far you can bend a note. So that's why I use .009's on my electric guitar. On my acoustic, I use .011 or .012 but it's very difficult to bend a note properly.....so I adjust my style. Just a fact of life.
Now, if you're going to stay tuned in drop C, it's a little different story:
With your current .012 string tuned to D, you have 18.52 lbs which is a little more manageable. If you go to a .014, you'll increase the tension to 25.01 lbs which even you may find a bit stiff.
There's a second factor to tension: scale length. A shorter scale length (distance from nut-to-bridge) will have lower tension. This is why it's easier to bend notes on a Les Paul (24.75") than on a Stratocaster (25.5") So you see, there are a lot of factors involved.
As far as the proper string gauge for drop C, you're on the right track. The idea is to look at the normal range of string tension in standard tuning. Then choose a strings that will fall within that same range when you de-tune to drop C. This will of course require heavier strings. Here's a link to a string tension calculator to help you determine the best gauge: http://www.mcdonaldstrings.com/stringxxiii.html