Sewing knitted stuff

Is there a way to sew knitted things without making a ridge? I used mattress stitch to sew some slippers and now they have a ridge on the bottom (not comfy because it is the bottom of the slipper). So I was just wondering what (if any) other methods there are of sewing so that a ridge isn’t made?

Thanks

:knitting:

I haven’t used this join yet but it looks quite straightforward. It’s like a baseball seam and it shows up at about the 5:00 minute mark on the video: