You could do some lunging at first, just a light jog, same as if you were on a light hack. At the barn I work at now, I'm keeping horses going through the winter by lunging light 20 minute trot sets every day, and maybe a light canter if I feel like they won't get too frisky.
You could then do some hacking out under saddle, maybe some hill work at that same light trot, just building stamina. I wouldn't start hard canter work (which builds air, mostly) until later in the winter :)
Exciting that you're starting back up!! How many days per week do you usually get to ride?
Every great dream begins with a dreamer. Always remember, you have within you the strength, the patience, and the passion to reach for the stars to change the world. ~Harriet Tubman