There are a couple of things people can do to maintain the egg supply during the winter. As you noted, some people add pullets to their flock each year, as pullets hatched in the spring tend to lay throughout their first fall and winter, while the older hens in the flock are taking a break...
I've never used lights or heat in the coop, as I don't want to push them to lay in the winter when there are other biological demands upon them.
The girls molt when it's time, lay eggs when it's time, and go broody when it's time. Broodiness is the only part of this that I may interfere...