The cutter/ruler combo is like these, available on Amazon, Nancy's Notions and some other places. I have one that is 6.5 inches wide. I like it a lot. Some people don't. One thing is you have to use steady pressure the whole time you push down on the cutter or it will skip. You might be able to learn to use this with your left hand with just a bit of practice.
http://www.amazon.com/dp/B00EXIACSU/...l_4rsa7grsh6_b
http://www.nancysnotions.com/product...uler+cutter.do
Think about checking with your doctor to make sure you can use the hand as much as you want to, to make sure you don't hold up the healing.