Sewing up the seam on a sock

by Julia
(Rochester NY)

Hello all. I'm an avid knitter and have given the loom a go. I'm working on a pair of socks and have made the first one. What stick do I use to sew up the seam along the top of the toe? I have tried half a dozen different stitches and haven't found one that I like. I want a smooth, thin seam, not the bulky one I'm coming up with. Maybe I need to cast off differently to produce a less bulky edge?
Any help would be greatly appreciated.
Many thanks, julia