I agree wholeheartedly with Onebyone. You most definitely want a topstitch needle. They have a larger eye and longer scarf. The scarf is the indentation in the needle that the thread lives in as the needle goes in and out of the fabric. A larger eye and longer scarf means less friction on the thread, and it won't fray and break.
I have the exact same machine, and when I had it on a frame, I used size 18 needles. If I went to a smaller size, I got lots of skipped stitches.
Hope this helps!