Keycaps
Keycaps are where many keyboard mistakes happen. A set can look perfect and still miss the keys your layout needs. Check ISO-DE or ANSI support, 60/65/75/TKL/full-size compatibility, profile and legends before you fall in love with the color.
Taller profiles can change the sound and finger feel; cleaner legends make a setup calmer. If your keyboard already works well, keycaps are often the most satisfying upgrade because they change the board every time you look at it.