Building a shop for an already live site

So I've already got my site live, and now I want to add a shop section to it. I tried to add Spree, and it completely swallowed my site. Before I delve into configuring it to not do that, I was wondering if anyone had a better idea?

Currently watching a tutorial to "Create a Shopify app in 5 minutes" on Vimeo. I hope this works