Puffin Divers just down Kerrera Sound from Oban has good facilities. Slipway, and moorings- which are free to divers along with diesel and petrol refuelling.
This has good access to some of the best cruising areas in the UK
They also have on-site bungalows that a very good - sleep up to 7 for £75 per night. Book early if you want therse though as they are very popular.
( they call them waterfront accomodation on the website)