Add 'show out of stock items' into a Shopify theme

Hi Everyone - Please could you let me know if you can help with this project:

My Shopify theme 'Puro 2.0' doesn't appear to have an option to 'Show Out Of Stock items'. (I'm surprised it doesn't have this feature like many other themes do but I can't find it in the theme settings) . When this feature is turned on it should behave like this:

1. For items WITHOUT Variants:
When products on the website reach ZERO stock then the product still remains visible on the website but with an 'out of stock' notice instead of an 'add to cart' button (whereas currently the product is just removed automatically from the website)

[IMPORTANT NOTE: This functionality does actually seem to exist already but the only way you can navigate to a product that is listed as 'Out Of Stock' is if you go via a search engine. Example page: https://www.locoskates.com/products/seba-cj2-prime-aggressive-black-skates-boot-only-pre-order - to me this suggests that the feature I need already exists, but is just hidden or need turning on!]


2. Items WITH variants:
I'd like items with variants to behave like that attached image. ie Variants that are IN STOCK show as normal and variants that are out of stock show a note in the option-box which says something like 'Notify me when available'


Ideally, I'd like to be able to turn the 'Show Out Of Stock Items' functionality on or off with a checkbox in the theme settings (just like you can with many other shopify themes)

PLEASE NOTE: I do not need the email capture functionality part built. This work is simply to get the website in order so that we have all the correct functionality to start using a 'back in stock' app.

Thanks. I don't understand the 'Budget' feature in PPH so I've just set it to £183. Please quote me a price when you respond, thanks!

:-)

Jake.