Hi Ariane! Thanks for your great comments, they always make me feel so good.
I am working with a circular that's 12 inches long, and a 2.5mm needle. This is my first try with a circular for socks too, but it's going really quickly, and I think it's easier. The Fleece Artist sock kit comes with a sock pattern that's meant to be done with circulars. The last Fleece Artist sock that I did was on 5 dpns. Once I got the hang of it, it was pretty fast, but the circulars are still faster. Maybe it's just 'cause they're Addis.
One warning though...Depending on the size of the sock, it might be a be a bit tight around the needle.
You can order them from Urban Yarns if you're interested in the Fleece Artist, or the Fleece Artist Website may be able to tell you where they are stocked in your area.
Their sock yarn is 100% merino wool, and is fabulous to work with.