Shopify Theme Modification for Product Add-Ons

Shopify Product Add-Ons Integration
I need my Shopify theme modified so customers can choose extra add-ons directly on each product page and have those selections flow seamlessly into the cart and through to checkout. The add-on interface must live right beside the “Add to Cart” button for maximum visibility and convenience.

I’m open to whichever input style—custom text boxes, drop-downs, checkboxes—best suits each product, as long as every selection is captured, priced correctly, and displayed in the cart, order summary, and admin panel. Please work natively within Liquid, JavaScript, and Shopify’s APIs rather than relying on an off-the-shelf app that might slow the store.

Acceptance criteria:
• Add-on fields render beside the main Add to Cart button on all designated products.
• Selected or entered values pass to the cart, checkout, confirmation emails, and order details unaltered.
• Theme performance and mobile responsiveness remain unaffected.
• All code is clearly commented and delivered via a theme duplicate or Git branch for easy review before publish.

If you have prior examples of similar Shopify customisations, send a quick link so I can see your approach.