I've looked at lots of B&B's, and have some ideas (more recommendations welcome). However, I had a great experience in Italy a few years ago with renting an apartment in Rome for a few days (cheaper, and we're fine without daily services/breakfast), and then at an agritourism locale outside of Florence (basically a B&B on an olive farm). Any unique lodging ideas for Edinburgh, Oban and/or Dublin/Dun Laoghaire areas? No car, three adults.
There are apartments to rent in all the places.
I personally haven't rented in those places but I am sure a Rick reader will post a site.
Vrbo is a good start.
http://www.aboutscotland.co.uk/edin/rentals.html
I had a good time at 25 Waverley Park, but it is more a 2 person flat, so you may need to look at the others. I think for each listing you contact the owner/agent (I dealt directly with an owner; she was very nice!).
25 Waverley does say it could fit 3 people. It has a double bed and sofa bed. If you are not too tall (I'm 5'5"), just sleep on the sofa. It was real comfortable!
For an Edinburgh B&B, I have also stayed at the Dene Guest House, http://www.deneguesthouse.com/ Great breakfasts and easy bus access.
Cheers.
We stayed at the Kimberely B&B in Oban this past summer. It was wonderful and I would highly recommend it. It was close to the center where we did not need our car and we could walk into town.