A short-sleeved bodysuit or summer baby pajamas underneath a lightweight sleep sack should keep them comfortable and safe through the night. If it's a particularly warm night then a footless sleepsuit or bodysuit on its own should be fine.

Whether sleeping or traveling, newborns can wear short-sleeved clothes or pajamas, depending on a combination of factors such as temperature, season, and comfort.

You can observe in several ways:
1. Cool hands and feet - If your baby's extremities feel noticeably cooler than the rest of their body, this could be a sign that they are losing too much body heat.
2. Goosebumps/Shivering - Shivering or skin that looks "goosebumpy" is a sure sign your baby is feeling cold.
3. Fussiness/fussiness - Babies who are too cold may have trouble settling and sleep restlessly. Fussiness or crying may indicate discomfort.
4. Curl up - Babies may try to conserve body heat by curling up tightly. Check for clenched fists and folded arms and legs.
5. Clampy skin – Skin that feels damp or clammy can also be a sign of a cold.