I walk with a cane and would love to be able to carry Topher in a bag, too. (He weighs 10 lbs)
I saw one at Walmart the other day that I might try. It was only $14.00Cdn and it was like a backpack only it fit on your front. I did try him in a couple of bags at a pet store once and he didn't like it a bit..lol..though we did try the one where the front and back legs stick out....he didn't seem to mind that at all and he didn't seem uncomfortable.
I'm still up in the air with what I'm going to do. If I find any great solutions, I'll be sure to announce it here.