I feel your pain. You are right, buying eggs would be head ache free, but then again we don't really do this because it's easy. We do it because we like a challenge, or because we love the animals, or because we value know where our food comes from and how it was raised. We have just gone through the absolute shortest days of the year - it's only going to get better from here.
Some things to think about:
I find that it is less about the amount of light, and more about the duration. If you are looking to make an adjustment in that regard, try to get them at least 16 hours of light a day even if it is not super bright. At the same time you don't want to just keep the lights on all the time - that's likely to stress them out.
With them spending more time in the coop and less time out foraging, have you found any evidence that they have taken to eating eggs? Sometimes out of boredom, sometimes because they are lacking some particular nutrient, but it happens.
Have you seen any evidence of someone stealing eggs, ie a rat or other critter?
It sounds like you have put quite a bit of effort into your setup, and I hope you manage to stick with it. Good luck and if you find something that makes a positive change, let us know. We all have our struggles, especially this time of year.