Hi Peat,
I live close to St Ursanne so i guess i can give a few tips
If you come by plane Basel is the best.
By train from Basel is nice but somehow slow (no hillclimbs in flatlands
). Take a train from Basel to Delémont and then from Delémont to St-Ursanne. For schedules -->
www.sbb.ch.
By car from Basel it's a very nice ride through the countryside, lovely roads etc.
For the hotel you will find a room if you don't wait too long. If there's nothing free in St Ursanne directly (it's a small town) you will find something in Delémont or Porrentry, they are the closest larger cities (max. 15-20 minutes by train i'd say).
My last advice : arround St Ursanne it's a very nice region for walking, the town itself is lovely too, if you spend a day for visiting the region you won't regret it