An infant carrier (sometimes called a Group 0+ or i-Size infant seat) is designed for birth to roughly 12–15 months, always rearward-facing, and light enough to carry with the baby still in it — useful for the sleeping-baby transfer from car to house.
Weight of the seat itself matters more than people expect once you’re carrying it (plus baby) up stairs regularly. A few hundred grams difference between models adds up fast over months of daily use.
Look for a recline range wide enough for genuinely comfortable head support in a newborn, and check the harness adjusts without unthreading as your baby grows through their first year.