Foot fit and shaft width are two different things
The boot holds your foot through its shape and closure. The last, the form the shoe is made on, determines, among other things, the width of the forefoot and the space over the instep. That is why a slim shaft can look narrow while your heel still slips inside the boot. Tightening the laces more will not reliably compensate for a shoe shape that does not fit your foot.
With laces, you can adjust the width in sections. They should not pinch over the forefoot, and they should hold your foot over the instep. If the model also has a zipper, it makes the boot easier to put on once you have adjusted the laces. A zipper-only closure, on the other hand, offers little scope for accommodating different instep heights. Covered edges and tongues must not create a hard pressure point.
When standing, your toes need room without having to grip. When taking small steps, your heel should not lift noticeably. Check both feet, since they can have different shapes. A larger size also means more length and often more volume. So if only the width feels tight, a different last may be a better choice than a longer boot.



