I have done three winter
caminos, and I disagree about "winging it"!!
Albergues in the cities will be open, but all the others will be surprises, and it may not be a matter of walking a few more kilometers. None of the internet websites are accurate on closings. Many that are listed as being open all year simply are not.
Hospitaleros do not wait around for a scattering of pilgrims, so call ahead to see if they are open. You should plan your stops, then adjust those plans for open
albergues.
Hoteles and
hostales, however, will mostly be open. I have found
www.booking.com to be very useful. Don't expect heat, but if it is cold, ask. The response may be a grudging response that will result in a few hours of warmth. Even the most charitable of
albergues will be reluctant to spend 20 Euro of energy for an 8 Euro bed fee. No one wants to lose money, which is why so many places will be closed. An operation does not break even on the winter crowds. You may be pretty much alone. I met only 12 fellow pilgrims in three weeks in January. It was fun, be be certain that you are self-contained enough to be comfortable with just yourself on the road and in the
albergue. I wouldn't see the point of turning a joyous opportunity to be out walking into a depressing funk.