Adding additional SKU codes

Hi all

First post, be gentle
I've been trying to sort this issue for a couple of days now. Normally looking through all the posts fixes whatever I need... but I'm stuck.
We have our shop up and running fine Version 1.5.3.1

We want to add a SKU code to the option selected that relaters to the size chosen. Each size of our products has a different SKU code. The main SKU in the Products >> data >> can be 001

I have seen some mods that say add SKU to the invoice, not really fussed about that we just want to make sure the SKU code is right for the product size, for our records and stock levels. Also I didn't want to install this as it was not for the opencart version we are running.

What do we want to achieve:-
Each size of our products has a different SKU code
The main SKU in the Products >> data >> can be 001

but in the Products >> options I want to set up the following
Size: small
SKU: 001-101
====
Size: medium
SKU: 001-102
====
Size: Large
SKU: 001-103

If anyone can suggest something for Version 1.5.3.1 which will do what we need that would be ace

Thanks in advance

This is exactly what I'm currently looking for there are some options out their but there all paid for add-ons, and I would rather not pay aha but what I have thought about is to just brutalise opencart's already in place SKU option within the 'data' area and use copy that it shouldn't be soo much trouble but saying that it probably is and time is of the essence :/

The options boost mod adds skus to options. Not sure if any other mod does, but this one I use and it works perfectly.