Grew up there, parents still there so know the local stuff well.
The mountains will either be very wet or frozen solid/covered in snow depending on the weather. More likely muddy as it’s been very wet in the mountains for a few weeks now. Some rides are doable as long as it’s not windy – the Gap is the most weatherproof option as it’s solid rock most of the way round. Ridden it in snow and ice without too much trouble.
I’d personally head to the Forest Of Dean, rides well in all weathers and it’s on the way home for you. Cwmcarn would be a good blast if you have the time as you’ll be going away from home to get there.
Depends if you want natural or man-made really!!