QTY Shipping Rules?

Hi all,

So having abit of issue working this one out. So my client http://www.justember.com has 2 types of products so far. One is a 2 piece cube candle set (hidden on the store currently) and one is a 1.3kg wax skull.

They want to be able to have the shipping based on 2 box sizes which cost different amounts to post. so they have a small box and a medium box:

So you can get up to 8 sets of cube candles in the smaller box for £3.20 delivery. If someone orders two skulls or one skull plus a set of cubes then it’ll be the medium size box for £5.30.

Can anyone help me with how id go about setting this up in woo, or a plugin i need for custom rules? Ive thought about a few options but they keep falling on their faces.

Even if i could set it up so the cart applies the shipping cost to total weight of the items been bought?

Thanks in advance!

The page I need help with: [log in to see the link]