Well, this does make me feel a little less guilty about spending £15 on a new to me Goth dress today...
I personally would go for the black stripey one - look at my username! I love that one. But choose which one you like. As long as it's comfortable and practical - and you can afford it - go for it.
From the Australian website, I'm guessing that that's where you're from? Barefoot bowls on the beach in a minidress probably makes more sense in that culture and climate. Have a blast, OP. And happy early birthday. 🎂