We just used a singlet and a nappy or a onsie. Sometimes if it was really hot just a nappy.
We swaddled our summer baby in muslin because he preferred being sweaty and wrapped and refused to sleep without a wrap no mater how hot it was.
Depends on the weather where you are - I'd sometimes start with both singlet and onesie for the cool of the morning, but if bub got too hot during the day off would come the onesie, or off with the singlet and continue with just the onesie...
DD did like her muslin wraps in the early days too.
We dressed our girls in a singlet romper or a short sleeved romper and their nappy. We wrapped them in thin breathable materials like cotton and bamboo (I think it was?)
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