My old stomping ground, Corfe Castle was home for a long time. That time of year some of the routes up on east and west hill might be a bit crappy in the way of views if the weather is poor, but tops are grass and the climbs and descents although chalky are also full of stones/gravel so grip shouldn’t be and issue. . There is a route from Studland in the new MBUK btw.
Or just up, along the top and down into Corfe. Greyhound is the better pub there, Bankes can be a bit hit and miss.
You could venture up the road to Wareham forests some good trails there but can also get a bit waterlogged.
Whatever you do, it’ll be sloppy and fun. But the views up on the hills are absolutely worth it.