For the serged seams, I decided to use wooly nylon thread for the upper looper. It offers a flexible and less bulky option then standard poly thread. With this fabric being more of a medium weight density, I wanted to be careful about the seams being too bulky.
I then sewed this serged seam flat. I selected a grey thread in the sewing machine needle and black thread in the bobbin. Sewing with the grey fabric on top, I used a lightning bolt stitch for a bit of stretch and sewed the serged seam flat, underneath.
To sew the seam flat, I used the standard sewing machine. I used a Dual Feed foot that came with the standard sewing machine.
I also adjusted the Dual feed balancing dial to a -3 for the fabric.
The following is the lightening bolt stitch that I typically like to use when sewing knits on a standard machine (stitch number 6 in the photo). You could also use a zig zag stitch for this step.