Shopify Website Enhancement

I'm seeking a Shopify expert to enhance my website with key features and improve functionality. The main focus will be on implementing an "Add to Cart" button across all product listings.

Key Enhancements:
- **Add to cart button**: The primary feature needed is the addition of a clear and functional "Add to Cart" button to every product listing on the website.
- **Endless scrolling**: I would like the endless scrolling feature to be activated on the Home Page.
- **Cart upsell bar**: You'll also be tasked with installing a cart upsell bar to encourage additional purchases.
- **Free shipping upsell**: The implementation of a free shipping upsell feature is requested.
- **Filter by size on collection page**: A filter by size option should be added to the collection page.
- **Sticky footer**: I want a sticky footer to be present on all pages. This footer should ideally include shortcuts to Home, Cart, Collections, and Account pages.

Design:
- For the "Add to Cart" button and other features, I'm open to your design suggestions. However, I do not have any specific requirements at this time.

Ideal Skills/Experience:
- Proficiency in Shopify and its features is a must.
- Prior experience with e-commerce website enhancement and functionality improvement.
- A good eye for clean and modern web design would be beneficial.