I don't mean to be obtuse, but I'm missing something here.
Timethief, you pointed out that Twenty Eleven does have default layouts that include a sidebar. I've chosen one of those, yet the sidebar disappears when the reader leaves comments. What I'm trying to figure out is whether there's a way to change that.
In other words, it's not a question of choosing the right layout. I've already done that. It's a question of keeping that layout on all pages, including comment pages. For some reason, Twenty Eleven is insisting on switching layouts for comments pages. Is there a way to change that?