Best installation practice advice please

Hi all

We currently have a brochure style site which lists products on portfolio pages. We would now like to integrate woocommerce under the same domain but still keep the current site as is with a link in the main navigation to the shop.

I have installed woocommerce, added some test products and the relevant base pages have been created.

The only issue I have is I would like the shop to appear as a separate site with a completely different main navigation.

So really my question is would you recommend a using a plugin to display a different main nav on the shop pages or would you do a fresh install of wordpress in a sub directory (/shop) and just run woocommerce on that? or even go down the multisite route?

It would be nice not to have multiple wordpress installs and pretty much two lots of the same media on the server, but if thats the best solution then so be it.

Any advice is greatly appreciated.