Sounds like you are already working towards a plan. Best thing not to let the dread of Winter, cold, lack of light just take over and get you down!
Being outside - my own favourite place and I hate any lack of sunlight - means that you WILL need suitable and practical clothing. Something for walking and both water and windproof so that you don't get caught out and you can enjoy the outdoors. If you don't already, do think about layers and start with some light thermals - long johns and a long sleeved vest once the days get cold. An extra fine layer of insulation like that next to your skin will do wonders when it's cold. Layers are a good idea so your outer layer should be able to accommodate items underneath for even the coldest days. Hats, scarves, gloves, warm socks. This should mean that your plan to go on long walks (join a Ramblers group ?) will work and you'll also be tempted to get out in the fresh air whatever the weather. Start your outside plans when it's daylight and be determined to always be back at home before it's dark. Put up some little welcoming lights outside? Why not think to make some changes to the inside of your home, think about a more Scandinavian approach, something along the lines of Hygge, the Danish 'cosy' description : have your home filled with comfy places to sit, no bare windows after dark, a corner seat next to books, possibly a heater or wood burner, some treats to eat, music playlists, think of a bath or shower if you come home cold, have soft throws and cushions handy on the chairs for fighting any draughts, and very soft and comfortable clothing to wear in the house and to relax in. Hopefully after at least part of any day spent out in the winter air, and having taken lots of exercise, coming home to your own warm space with nice lighting might encourage you (sometimes) to put up your feet and watch something you have chosen on t.v., or spend some time with friends, playing old fashioned games perhaps, or cards, or a glass of wine. Maybe in this way, once you feel prepared, it's more likely you'll feel you can face winter head on...without feeling that you're trapped indoors looking out at too many short days and darkness.
🍂🍁❄️ 🌷🌞