So your birds are older?
A 6 year old bird might be a favorite pet, but isn't going to lay many eggs.
The 2 year olds were 1 year old (or less) pullets last winter, and probably did lay eggs through the winter. But as 2 year olds, they probably did a molt and have now taken a few months off. They probably will resume laying some eggs (not as many as last year) in a month or so when the days start getting longer. So the solution continuous eggs is to turn the flock over on a regular basis. New birds each year to replace the 2 year old girls at the end of the upcoming summer. So long term, your birds are on a continuous rotation in and rotation out........at least if the goal is eggs.
Extending the day by adding light may help your current birds in the short run, provided you have met all the other requirements of surviving in winter conditions while still producing eggs. Shutting down is in part a built in safety device for them to enable them to concentrate now on winter survival. Nearly all commercial flocks use supplemental light to keep them laying, but they burn through their birds pretty fast. In a commercial flock, your 2 year old birds would already be gone.
If I was to add light, it would be inside the coop and would be set on a timer to come on in the early morning hours only. Let the day end as usual to let them ramp down the day during the normal evening dusk, such that they go to roost. To put in on a timer to shut down suddenly after dark might leave them running around lost in the dark.