Questions & Answers about Kamar kos saya sempit, tetapi nyaman.
Kamar means room. Kos (often written kost informally) refers to a rented room in a boarding house/rooming house (common for students or workers).
So kamar kos specifically means a boarding/rooming-house room, not just any room.
Saya means I / my in a neutral-polite style. In kamar kos saya, it functions like my: my boarding room.
You can use aku in more casual/intimate contexts: Kamar kos aku sempit, tapi nyaman.
Both are grammatical; the choice depends on formality and relationship.
Indonesian often omits the verb “to be” in simple descriptive sentences.
So Kamar kos saya sempit literally reads My boarding room (is) narrow/small without needing a separate is/are.