Hi There

In my searches of the forum I have been unable to find info on the following:

I have items for sale which are categorised firstly by colour, then they are broken down into size L,XL and XXL. I have linked them using the attributes controller, optin name and values.
My issue is that I have postage of €15 for the first item. once the purchaser buys more than 1 we drop the postage rate to €7.50 for each additional item.
Example:
1 jersey costs €60 with postage of €15 total = €75.
if my buyers wnat to get 2 jerseys it is then going to be €120 for the jerseys €15 for the first one and €7.50 for the second making a total bill to the buyer of €142.50.

Am I making a very big mess of this or is there a better way of organising this?

Any help is greatly appreciated.
I have Zen Cart 1.3.8a installed