What you need is a multi generational flock. Each year you have to cull some birds, and add some birds. You want this years chicks to start laying by September... and they will lay through the dark days of winter. Of course their eggs will be smaller but you do have fresh eggs.
My older girls will start laying about the end of January/February given some good sunshiny days. Their eggs will be bigger than the pullets, but the pullets will go to full size. Once my older girls molt, they seem to do it just as the days start getting noticeable shorter, and won't lay again till spring.
I should cull during the molt, cause they look old and tough then, but I didn't and now they have those nice new shiny feather and look just young again! haha
Mrs K