Hi C - lots of choice in the area for accommodation. Posh one is the Western Islea Hotel overlooking the town, as well as a good choice of more modest B & B and small hotel accomm.
Remember the wahale sightings are seasonal - more towards the warmer months, so be prepared for a nice bit of planning before travelling - allpart of the fun?
Also where are you travelling from to get to the Isle? The ferry from Oban docks at Craignure in the south of the Isle - worth a trip to Iona if you fancy seeing a bit more of the place. Dervaig is interesting, and the distillery in Tobermory is worth a look to - only for research of course.....
There are a some nice small hjotels in the harbour itself at Tobermory or those above the town offer views over the loch. And the fish and chips from the van on the quay are worth the journey alone. Go on, spoil yourself! It actually has a Les Routiers award................honest....
http://www.silverswift.co.uk/van.htm see........!
http://www.jenny.mull.com/ is one w/watching company and there area few others in Tobermory to choose - see the TIC site at:
http://www.visitscottishheartlands.com/areas/o ban/index.cfm for area info - should be able to get a good feel for the accomm. and what to do from there.
Also some companies like:
http://www.seescotlanddifferently.co.uk/specia l-experiences/24/itinerary-9/ can arrange whale watchig as well as the accommodation in a package to make it a bit easier.
Have a good time!