+1

Another option might be to sign up for a local spinning class or two ... if you get a good instructor, those can be quite challenging workouts.

And of course, get some warmer clothing ... and go ride outside!! I rode year round in the Canadian prairies. If the roads were particularly icy, I rode my trainer inside or went to spinning classes, but if the roads were even partially clear, I rode outside ... and there is no such thing as "too cold".