Squarespace Print-Size Selector Integration

I’m ready to extend my Squarespace photo-print store so each image shows only the sizes I choose for it. On the back end I need a simple panel—checkboxes are fine—where I can tick whether a photo is offered as a square, a standard 5:4, or one of my wide, narrow landscape formats. Whatever I check should appear instantly on the product page as attractive, shop-style option boxes that a collector can click to add that size straight to the cart.

Everything must remain native to Squarespace Commerce (no external checkout) and fit seamlessly with my current template. Clean HTML/CSS, a dash of JavaScript, or the Squarespace Dev Mode API are all acceptable as long as the solution is lightweight and easy for me to maintain. Future enhancements are already in the pipeline, so clear code comments and a brief how-to video or guide will be part of the hand-off.

Deliverables:
• Custom interface in the product editor for toggling size availability
• Front-end size selector styled to look like in-store swatch boxes and fully connected to the cart flow
• Installation and styling on one product as proof of concept, plus instructions so I can replicate it on the rest of my catalog

Once this foundation is rock-solid we can move on to the next features together.