Observe the gap in movement
Fasten the shirt normally and look at it standing, seated and with your arms reaching forward. Does the opening sit across the bust, at the waist or only when you move? Check whether the fabric pulls elsewhere, including the shoulders and upper back.
Button spacing can matter alongside overall room. A shirt may feel comfortable but have an inconvenient gap between fastenings. Another may be too restrictive across several areas. These are different situations and do not necessarily call for the same adjustment.
Compare shape as well as size
Try another size to see what changes, but check the collar, sleeves and shoulders again. More room in one area may create excess elsewhere. A different cut, dart placement or fabric may provide a better result than simply moving upward through the same size range.
Wear the underlayer you intend to use with the shirt when assessing it. A smooth camisole can change how you feel about an opening, but it does not remove strain from an undersized garment. Choose it because you like that combination, not because it hides an unresolved comfort problem.
Treat fixes as specific decisions
An added fastening may help a shirt that otherwise fits, but its placement and the cloth's strength need consideration. A tailor can assess whether a discreet closure or another alteration is practical. Do not assume every gap can be repaired without affecting the way the front hangs.
Avoid making your body the problem to be corrected. Shirts are cut to different proportions, and some will simply suit your movement better than others. Keep the one that works when you sit, reach and breathe normally, rather than relying on a carefully arranged pose to keep the front closed.
