From The Modern Sewing Co.:
The Sunday Trackies were designed for days where you want that extra level of comfort. This design is unfussy, roomy in fit and intended to feel like a second skin on a sleepy Sunday. It is a simple piece to make which means it’s a great project for beginners.
Construction techniques: Simple stretch stitch seams and a small amount of topstitching.
Sizing & Fit: This style is fairly roomy and slouchy so it is a forgiving garment in terms of fit. Choose the size closest to your measurements and don’t worry if they don’t match perfectly as the jersey fabric and elastic waistband will do the fitting work for you.
Recommended Fabrics: Jersey fabric (fleece or french terry). This style also has the potentially to work in a soft wool.
Sizes: UK 4-28