How to calculate shipping costs for the world?

Hi,

I'm working on setting up my commerce site through Squarespace and I'm wondering how you all calculate your shipping costs for the world? 

I sell products of all sorts of different sizes and weights. Setting costs for different weights based on every country's shipping zone in the world would be way too much work. I currently have shipping zones for Canada and the US, but past that, how should I set up shipping costs for the rest of the world?

The options I've thought of are:

1. Don't allow shipping to those countries. Let the customer know that they will have to contact me for purchases.
2. Create a flat rate for countries outside of Canada and the US, and then email the customer that they will need to pay more for shipping if they, let's say, happen to live in Australia. Not a fan of this one.

What do you do? Are there better options?