I'd go with B+, as long as there are still stores in the hive - hence my query about the overall weight of the hive now.
As Dishmop, bees often cluster/start to brood to the warmer side of a hive, but with the weather being unpredictable and generally cold again, you don't want the bees to run out of food against the wall...
If things are looking dodgy, I prefer that they have stores on both sides of the cluster but, to ensure that, you would have to pick a day and open them up quickly to shuffle the frames . Don't pull any out, except those with stores that you want to move, then slide the frames with the cluster over (if propolis/castellations allow...), and put the stores between the cluster and the wall, (and next to the cluster on the other side, if necessary).
Course, if there are no stores in the hive, this won't be possible. If you're not sure about this by hefting, do you have any spare frames of stores in storage(!) that you could have to hand, just in case?
I've not used it, at this time of year, but I have been told that Ambrosia or similar can be used all year round. They would be able to take that down from a contact feeder over the frames (during warm spells, anyway), but I would be a bit concerned about syrup being forced out of the feeder with contraction/expansion as the temperature varies. I am sure that someone else here will be more knowledgeable and be able to recommend yay or nay on this point.
If they are isolated - or just plain starving - it's better to do something now, rather than wait till it's warm enough to inspect a colony of dead bees....