Bright daylight bulbs, or good colour changing bulbs to simulate sunshine.

When it is bright outside, go outside and get some sun! Even if it’s cold, you’re still going to get some benefit.

Get an indoor air quality monitor. Open your windows and let in as much fresh air as the outside temperature allows. Cold weather = people don’t open windows = carbon dioxide and other shit builds up inside.

Circulate air with fans or central air set to fan only.