How to integrate BigCommerce' headless ecommerce functionality into existing next.js app?

Question

I have a website built on next.js and would like to implement BigCommerce' headless e-commerce solution. All the documentation seems to center around launching with Vercel or basically suggests you build the project around the original package provided by the repo - but what if I want to just add the functionality to my package? I'd love implementation suggestions from anyone who has already successfully done this.