Shipment rules based on weight and price. Override rule?

[CPHAGEN_Nordic]

I am experiencing an annoying situation with Shopify checkout system.

website: www.cphagen.com 

In countries where I offer free shipping about a certain amount, I would love the system to take in consideration the weight of the purchased good.

Ex: the sofa in the screenshot below is above the "free shipping rate" based on the price BUT it's way too heavy to actually be delivered for free! 

Is there a way I could say to the system: weight override price limit? 

Problem is that someone could purchase plenty of, exemple, nice jewels and reaching very high amounts.
But that is light and easy to ship.

Same can't be said for big and heavy furniture.

I hope I have been clear.

Thank you very much for your help!