I don't get why people expect a newborn baby to sleep "through the night". Their tummies are about the size of a gold ball. They don't hold enough to fill them up all night. We fed our dd solids at 5 mos after much pressure from her ped to feed at 4 mos. She developed food allergies and eczema. We held off until 6 mos and she was sleeping through the night well before this time (maybe at around 2-3 mos) ONLY ON BREAST MILK. Can you imagine?? After that we didn't listen to the ped when it came to starting solids. My son, my youngest, didn't get any solids whatsoever until 9 mos but you can bet he was sleeping through the night way before this (only on breastmilk). And on breast milk he was in the top percentile for weight so contrary to what some people thought, I wasn't starving him by not giving him solids-he was in the upper percentiles for weight on only breast milk.
And to keep it on topic he was in a sleep sack also for sleeping.