How can I set up different package sizes for shipping calculations?

I’ve begun to have issues with this.

My default box must be big enough for my biggest products, lest I lose much shipping money. But, then, for my tiny products, my clients get way over-charged massive amounts for the same, oversized default box. (I’ve had to refund some clients & lost money on others.)

So, Shopify can’t determine different Shopping Cart Check Out boxes to match the product?

Boxify is way to expensive to add to my Shopify account.