We stayed at Smithy Cottage (which is on there but has its own more detailed site tayvallichcottages: Welcome
) this year. Basically a very nice spacious 2 bedroom (4 person) cottage which has a wooden "challet" in the garden that could sleep another 4. Theres a couple of rowing boats free of charge (which may not be of interest but help keep any littl'uns amused). Its main attraction for us was the Jetty/Pontoon.
The owners also own Anvil Cottage and another, which don't officially get access to the Pontoon but there was a running mooring set up for anvil cottage which would be fine with your size boat.
It wasn't cheap, but for the capability to sleep 6+ people then in peak season this was not bad. Considering you've no marina fees (other than a small donation at the public slip) it is pretty good.
In previous years (I think this was our 4th trip) we have stayed at the Steadings which also nice but isn't on the water side so not so convenient (last year I set up a temporary running mooring but it was a bit of a PITA as the harbour is so crowded and all the "good spots" are already used). If the weather was OK you can possibly keep your boat afloat at the Carsaig side (direct into Sound of Jura) but its not very sheltered. I think I saw a sign at the main visitors pontoon at tayvallich that they were now allowing overnight mooring at a small part of the pontoon (never previously been allowed). Not sure what the costs are or how busy it is etc. Jambo might have a better idea. The pontoon is only 5 minutes walk from almost all the cottages in tayvallich.
Whilst tayvallich is just about perfect for us, it might not be everyone's cup of tea. We took the inlaws for a long weekend a few years ago, and whilst they liked it I think if it had been for a week they would have gone crazy. They are more cruise ship type people though!
As another alternative if you wanted to be a little further north, then we used to keep the boat at Linnhe Marine (www.linnhemarina.com
) who would provide pontoon/moorings for your stay (I think he was charging £10/nt last time I was there). Very nice guys, running a tiny little family business. I think they had cottages of some sort (if not they will certainly know some) - immediate proximity to a pub may be an issue for any that are close to the boat. 10 minutes north of there we have also stayed at Kentallen Lodges which were OK but are now under new ownership so I can't confirm what they are like now. They are on a small hotel site, with a tiny harbour. The hotel has a small pool which might be useful with kids. If you are not out on the boat though - you will need to drive to do anything from there as Kentallen is essentially in the middle of nowhere (although it is on the main road).