Thank you everybody for your pieces of advice. I've been combining extra-layer and sporran for my monthly party, as I was in a hurry, and I'll try to find something more suitable for next time.

The problem here in Paris is that anything looking more or less "scottish" is sold at high prices, especially when composed of wool... Also, the only place I found some tartan cloth (aside from high-end taylors and their "400€ greatkilt") was the Marché Saint Pierre, where a lot of cloth is sold, but they do not have anything combining tartan AND wool...
I've taken a look at Pendleton, but I didn't find anything really interesting for me, maybe I searched the wrong way, I'll see next weekend.

I'll post a picture of my "costume" in he appropriate section if I can get one from my friends, just to see what you think of it !