The received advice is to paint everything white. That is half right and it is the wrong half that gets applied.
Continuity matters more than lightness
A small room reads larger when the eye is not stopped — one floor material running everywhere, one wall tone, one ceiling. Three different floor finishes in twenty-eight square metres subdivides the space visually and makes each part feel smaller.
That is why an all-white interior often does work: not because white is light, but because it is continuous. The same continuity in a warm mid-tone works just as well and feels less clinical.
Run the floor through the threshold
The single most effective trick in a compact house is the same floor level and, where possible, a similar material inside and on the terrace. The eye reads the two as one space and the house borrows the outside.
It also removes the threshold, which helps everyone with anything on wheels.
Timber wants restraint
Wood on every surface in a small volume becomes oppressive by about the third surface. One elevation of timber against plainer walls reads as warmth; four elevations reads as a sauna.
Keep the ceiling the lightest surface. A dark ceiling in a two-and-a-half-metre room is felt physically, not just seen.
Reflection is a tool and a trap
A mirror opposite a window doubles the daylight and the view and genuinely enlarges the room. A high-gloss cabinet front near the same window shows every fingerprint and every reflection of the extractor hood.
Matt or satin on the large surfaces, reflection reserved for one deliberate place.
Texture carries a small room
With little floor area, the surfaces are close to the eye, so texture does the work that scale does in a large room. A woven blind, a linen curtain, a rough plaster or a brushed timber grain give the interest that pattern would give elsewhere.
Pattern, by contrast, is best kept to things you can change. In a small house a bold permanent pattern is unavoidable in a way it never is in a large one.