I like making my cookies larger myself, just to give more of a bakery aesthetic. Those cookies look great and I'm sure Brendan will be very happy with them
Golden syrup needs to be more commonly available in grocery stores. I actually found it in the international aisle of the grocery store by where I live at university. That store's international aisle had a section for British imported pantry items, which I thought was really neat. Unfortunately it seems to be pretty inconsistently stocked in stores here, and I haven't found it anywhere I've been to yet, without going out of the way to a store purposely just to get it. And it's pretty expensive on Amazon - $15 for a 1lb can or $23 for a 2lb can are the cheapest, because of the shipping. I definitely regret not buying it when I had the chance.
I've also seen some recipes online for homemade golden syrup, such as this one
https://www.internationaldessertsblog.com/make-golden-syrup/#mv-creation-7-jtr. I'm not sure how close it is to the real stuff though. It's simmered with a slice of lemon for 45 minutes, which looks to be how they invert some of the sugar and probably also contributes to the golden syrup flavour.
But there's also the confusing instructions where they write "If your syrup dries out before it turns golden, the problem is that the water evaporated before it reached the caramelization temperature." Unless if I've massively misunderstood making sugar syrups, isn't the temperature of the syrup directly tied to the concentration of sucrose in it? And at caramelization stage, it's 99% sucrose, i.e. almost no water. So in order to get caramelize it, the water
needs to all evaporate!