Match the layers by thickness
Begin with a shirt that sits comfortably on its own. Put the knitwear over it and check the upper arms, shoulders and elbows. A fine jumper over a very roomy shirt often reveals folds and feels more restrictive than expected.
Try a lighter shirt or a roomier knit before changing sizes indiscriminately. You want space for the fabric, not a second garment that is uncomfortable in a different way. Smooth the shirt sleeves once, then move normally to see whether they stay in place.
Choose which details to show
A collar can sit inside or outside the jumper neckline. Compare both rather than forcing it into a familiar formula. A soft collar may collapse beneath a tight crew neck, while a button-down collar can stay more contained.
At the wrist, a little shirt cuff may be visible or completely covered. If the cuffs bunch, loosen the jumper sleeve rather than pulling the shirt tightly down your arm. Check that a watch or bracelet is not caught between the layers.
Decide what happens at the hem
A tucked shirt creates less visible layering at the bottom, but adds fabric at the waistband. An untucked shirt introduces another line below the jumper. Look at the front and sides to make sure the curved shirt tail falls as you expect.
Finally, add your coat and carry your bag. Two comfortable layers can become cramped beneath a narrow coat sleeve. If you are dressing for a warm indoor space, choose a shirt you are happy to wear when the jumper comes off.
