Project: Sticky "Add to Cart" Button with Quick View & Checkout Flow

I’m looking for a developer to build a custom feature for my Shopify store (only 3 products):

Goal:
Create a sticky “Add to Cart” button (see screenshots) for desktop and mobile. When clicked, it should open a modal window with:
– Product image gallery
– Size selection
– Direct add-to-cart option

After adding the product, the checkout drawer (see third screenshot) should open automatically.

Requirements:
– Fully responsive
– Fast loading
– Clean integration with existing theme

To apply:
Please send:

Relevant references (Shopify work only)
A fixed-price offer with timeline