Outfits
A roll-neck under a blazer
Choose the knit for the space inside the jacket, not only for its colour.
Start at the neck
A roll-neck changes the area that a shirt collar normally occupies. Try it on before adding the blazer and decide whether the neck feels comfortable when you turn your head and sit down. A collar that needs repeated folding or pulling is unlikely to become easier under tailoring. The height and tightness of the neck matter as much as the size on the label.
If you prefer less fabric, a shorter folded neck may suit you better than a tall, substantial one. Do not force a dramatic shape simply because it looks striking in a photograph. The blazer already frames the neck, so a quieter knit can still create a distinct alternative to an open shirt or tie.
Leave space through the sleeves
Fine or moderately light knitwear usually fits more easily under a jacket than a chunky jumper. That is a question of available space, not a rule that fine fabric is always better. Put both garments on and bend your arms. If the sleeve lining grips the knit or the jacket feels tight at the upper arm, choose a different pairing.
Look at the back and the buttoned front. A blazer that fits over a shirt may pull over a roll-neck even when the neck itself looks tidy. Sizing up the knit will not solve that problem. You need either a thinner layer or a jacket with room for it, while still preserving a shoulder and sleeve length you like.
Use the contrast deliberately
Charcoal knitwear under navy creates a close, subdued combination. Cream under dark brown or navy gives a stronger frame. Black can be striking, but check the whole outfit rather than assuming it works with every blazer. If both surfaces are very smooth and dark, textured trousers or a softer shoe can prevent the result from feeling overly severe.
A roll-neck does not require a necklace, pocket square or other detail at the opening. Let the changed neckline be enough at first. Once indoors, make sure you are comfortable if the blazer comes off. The knit should work as a complete top, with a hem that sits well over the trousers, rather than being chosen only for the small triangle visible beneath the jacket.
