On Friday I popped into John Lewis and bought myself the Janome Ditch Quilting foot (aka Stitch-in-the-ditch foot) for £13. As you can see from the picture, it has a handy black plastic guide which enables the user to easily see where their stitches are going. I used stitch width 3.5 and stitch length 2.4 which I tested beforehand to make sure it was suitable for all those layers. It took a fair bit of adjusting the tension (and me interpreting the pictures in the user manual wrongly!) fo me to get it right. However, once on it worked a charm and made the job of sewing over the square seams so much easier. I'm going to buy one for my mum!
(Janome DC3050 is a Cat B machine and uses snap-on feet.)