Hmm, I think this is a quite a task to take on, You are basically reproducing a segway and Im pretty sure Human Like movement based on balance is not an easy thing to pull off both programming-wize and mechanical wize. Its going to take a lot of effort to pull it off.
On the hardware side:
Ive seen balancing done with distance sensors as well though. Where they point at the ground and measure the distance difference between the 2 sides and make movement decisions based on that. And, I dont know much about the speed of the microcontroller that you need to accomplish this feat but I imagine that it needs to be pretty fast and update often.
Sorry I couldnt be more help, but good luck! and I hope to see it working
