Hi. I'm not a Business user, so there may be more sensible ways to do this - but my suggestion would be to export your notes to ENEX. You're correct that export does not save the notebook connection - and therefore also ignores stacks. There is an option in the Legacy Evernote app (Tools> Options> Note> Note Merge Options in Windows) to vary the size of the 'chunks' into which an Enex file is split, but you would need to export one notebook at a time. Make sure you check the export options too, because tags should be included.
The only other option would be to share your notebooks to the business account, but I don't know whether that is even possible. Again, there's no stack-level share so you would have to reassemble your layout in the Business account.
Hope that helps...