Render NextJS app in a Shopify storefront?

[colchuck]

Hello dev community:

I am new to Shopify app & customization and with the amount of options that Shopify provides I'd need some suggestions here.

I am looking into rendering an NextJS app (React UI + NodeJS BE) in an existing Shopify store of mine. The app I am building will:

1. have auth access to my store's storefront API and potentially admin API.

2. have some UI that will be built with polaris and be rendered in my Shopify store as a dedicated module, not as a block. Imagine there's a flyout that can be called inside some certain pages of the store. 

3. be for my store only, I am not looking at getting it enlisted in the app marketplace. 

4. I will host my app in AWS but am open to other possible hosting options that work better with Shopify.

Would anybody provide suggestions for a path forward? I looked into Shopify embedded app, app proxy and Hydrogen and Oxygen. Hydrogen and Oxygen is a bit of a overkill because I do not want to build the entire storefront from scratch, my partner wants to leverage Shopify wysiwyg and templates to build the store himself. Embedded app or app proxy seem to be promising but I am not sure if it checks all my checkboxes.

Thanks in advance, anything is helpful! And please, drop me a line if anything is unclear.