Irrespective of local conditions, the first thing to do is to establish whether or not feeding is required.
That can be done firstly by visual inspection.
Having seen what the stores level is, learn what that feels like to 'heft' - or give yourself a means of attaching a luggage scale and measure the weight of what you've seen.
You should aim for 20kg/40lb of stored honey (beyond the weight of the hive and frames). Thats a single-brood national pretty much stuffed full.
If you *need* to feed, then its strong syrup (or better Ambrosia-style strong invert syrup - less water to remove and non-fermenting, never mind the invert sugars), but when the bees lose interest in it because it's too cold, if you are still light then it has to be fondant.
Hopefully you have plenty ivy nearby and your weather is allowing the bees to harvest it for themselves - saving you the cost of some sugar/syrup.
No bad thing to have a see-through crown board so you can visually check during winter without fully opening the hive.