The vilene is good but Sulky has a heavy duty you can get from Joanns as well. I've even used a double or triple layer of the one the sell on the bolt and it worked well. For FSL, try using a sharp needle and lower the speed and that should help. It took me many tries but I finally even got the cone serger thread to work. It was for things for kids and I didn't care about the sheen, I just used these tips plus a larger needle. I also like Floriani thread.