Heavier thread weights can sure work to advantage when doing satin stitch! I've been adding lettering to some quilt blocks, and practicing on scraps using different fonts. I print out the size I want from WORD and then trace the letters onto fabric. Putting two layers of tear-away stabilizer underneath my work means I don't need to use a hoop. Originally, I started with 50 weight thread going over the stitching twice. Then I switched to a 28 weight thread and found it fills in the space between the stitches really nicely with just one pass. This is Aurifil colour 2725, a pretty soft blue. The needle is a size 90/14 metallic, which has an extra large eye. 50 weight thread in a matching colour is used in the bobbin.