Page – two post boxes on one page

I’m making a website with WordPress as a CMS but without the WordPress front end.

One every page of the website there will be an article, and a sidebar with extra information and images. So what I need is a double post box on the WordPress “edit page” page – one box for the article and one for the sidebar content. They should both have the full editing possibilities (e.g. making text italic and inserting images and links), so simply using the exerpt field is no option. Does anyone know a plugin that does this, or another solution? I can’t seem to find it…

Thanks!