Sweater almost done

Hello Everyone,

I have the 4 pieces of the sweater done. Now I am to
sew on the left sleeve. I don’t want to use the mattress
stitch as it has a bulky seem on the inside. Is there
a popular sewing seem I should know about?

In my experience, if you do mattress stitch using only the very edge stitches, it produces about the neatest seam you can get. Honestly I don’t know what else you would use.