Here is something you might like to do. As you will be on the Jacobite which arrives in Mallaig around lunchtime, stay in Mallaig for lunch and then get on the ferry to Armadale on Skye. From here you have quite a few options. There are buses to Broadford, Portree or even Kyle of Lochalsh. All these places have lovely hotels and B&B's. Or stay in the Ardvasar hotel, close to the ferry terminal. The Ardvaser is a cracking wee hotel, really West Highland!
Alternatively, you could arrange the small passenger ferry to Inverie on Knoydart and stay at the Old Forge. This is a truly wild and wonderful place to stay with the guarantee (almost) of sampling some local entertainment.
All these things are very do-able as you have said that you only need to make it to Corrour or Rannoch and don't forget that in June it is still quite light at around 11pm up here! Mallaig has loads of good accomodation also.
Corrour is very limited with only a bunkhouse (not sure if the restaurant and bunkhouse is still going here), same with Rannoch. The Moor of Rannoch hotel is the only hotel anywhere near the station but is still a very nice hotel. Further South you have Bridge of Orchy (The Bridge Of Orchy Hotel), Tyndrum with a couple of hotels and Crainlarich with plenty of places with good accomodation.
Oban itself has a multitude of Hotels and B&B's, but try and aim for one on the front as these afford the best sea views.
Finally, my last tip for you would be to speak to someone at Visit Scotland and explain your itinery. They are absolutely brilliant at finding you accomodation and any deals going. Trip Advisor is good but don't take everything you read at face value as the West Coast hotels aren't everybody's cup of tea. If you like friendly locals taking over the bar with the odd instrument or two then you will love it!
Enjoy your trip and if you get the weather, it will be a cracking wee holiday for you both but bear in mind it is midge season in June and the West Coast midgies are ferocious!
