Swaddling. In my experience with many babies under 4-5 months, swaddling helps so much to get babies to sleep longer, and more restfully. Often, parents think that babies are struggling to break free of their swaddle and that they will sleep better unswaddled, or with their hands up to their face, but my experience has taught me the opposite. When babies have their arms free to move about while they sleep on their back, they startle frequently, and that startle reflex disturbs their sleep and causes more frequent awakenings. When they are swaddled, but with their hands up close to their face, this usually initiates the rooting reflex, and they start sucking on their hands and start fussing to be fed, often at even closer intervals than I recommend feeding them during the day. My favorite swaddle is the Miracle Blanket because they stay swaddled better, it’s better about not riding up on their face (which makes it safer, in my opinion), it’s not too hot or thick, and it’s easier to transition out of than many other swaddle blankets.
Sound Machine. I love using a sound machine to help in sleep training babies because I think it helps them sleep longer and more restfully since it blocks out noises that might otherwise disrupt their sleep. Parents are often concerned that their baby will become too dependent on it, but it’s one of the easier things to wean from, if you just slowly start turning down the volume over several days. I also recommend putting your baby in a different environment to sleep 1-2 times a week, anyway, without the sound machine, out of their crib, and with more light and noise than typical, so that they can sleep in other environments. I do like keeping them in a dark, quiet, familiar place for most of their sleep, to help them get better quality sleep most of the time, but flexibility is also important for being able to nap in varied environments.