I think that this Magento 2 Out Of Stock Notification is suitable for your requirements.
Magento 2 Out Of Stock Notification is a helpful and versatile tool to supports & keep your customers updated.
The Out Of Stock Notification Extension assists you in notifying the customers who come to your Magento 2 store about all the changes that happen to the stock on the store including stock notification, changes in prices as well as the status of the stock.
- [New] REST API Support
- Customer can subscribe notification for: Out of Stock Product, Sale Off Product,
- Change Price Product
- Notify customers by-product (product stock status, price changes)
- Notify By Email Automatically or Manually FEATURED
- Customizable Email Template
- Subscribe unlimited individual products
- Manage the list of subscribers easily
- Display stock alert in a popup or on a page
- Display notification any page
- Choose to subscribe or unsubscribe with ease
- Show Advanced Report: Out of Stock Product Subscription