post hierarchy – need to put "post child" into "post parent"

Hello,
I have a specific issue – my client wants a site built on wordpress with following feature: It should have categories (i.e. “furniture”, “computers” etc.) with posts (i.e. “chairs”, “tables” etc. – it has to be posts because it has to have comments feature) and – which is the problem I cannot figure out – these posts need to have “sub-posts”. In another words: I need to have option in admin area to add posts (or something like post where I can fill some field and date of expiry) and have a possibility to associate them with the “parent” post (those “chairs” or “tables”) and display it in the “parent” post. I hope I was clear enough, it’s kinda hard to explain. Do you guys have any advices for me?
Thanks,
John