shipping classes

Hi everyone, I’m trying to work this out but have just got myself in a mess (and I am perhaps overthinking it!?)
What I’m trying to do is create the shipping for individual items in my online shop (not launched yet).
To explain further, I have 2 different categories of items:

category 1 – small items (that fit in a small bubble envelope size (‘Large Letter’ category in the UK); and
category two – large items (i.e. in a 45cmx45cm box type of size).

I also want to make two postage options: UK and international.

Within the UK, I’d like to have the option for the category 1 items to be 1) Free postage; 2) expedited (First Class); and 3) Tracked (Courier).
Internationally, for category 1 items I’d like options for: 1) International Standard; and 2) International Standard Tracked.

Using the above as an example to get me on the right track (hopefully, please can someone help?!), how do I create this situation so I can select it only for my type of products that I want?

As I say, I thought I was doing it correctly, but what I’ve done isn’t working as planned!