Product detail page: optional related product and text accordion

[al404it]

I'm new to liquid and theming and I'm kind to find a way for customers to buy an optional product connected to main product.

For example: a bookshelf that can have as an optional connected product a light 

What I would like is in product page add something similar to buy button that open in overlay

Not sure if is possible to hardcode something like this in theme based on product collection

I have seen that some theme like this

https://betty-theme.myshopify.com/collections/totes/products/city-sol

have accordion at bottom of product description, how do they handle input in product backend since products has just one description field?

[CANDISOFT]

- if you have limited products then you can use different product-templates to show different contents on each product page.
- but if you have a lot of products, then you will need to use metafields app to render different content for different products.