Well, I would probably just use the code from the twentyeleven theme and use the have_comments loop. But, if you want to go this way, you could grab the post ID first, then put it into get_comments. Something like this:
I figured it out shortly after making this post. I used get_the_id to figure out the post id. For some reason when I try post->id it returns things badly. I am using the chunk of code above inside the loop. So this works well
Then you can use:
I changed the '$post_id to $post->id that should fix the error.