You likely want to get your infant to sleep through the night. Help facilitate this by bringing your baby to the breast more often (e.g. every 2 or more hours) in the early evening helps your baby store up on much needed calories so if they are ready to sleep a longer stretch they will be able to achieve this. The hind milk, which makes up more of the proportion of breast milk in the afternoon/evening, is made from rich fatty milk that has lots of calories to help sustain longer sleep for infants. Introducing formula and/or solids has not been shown in research to help with sleep.