Cornwall:
YES! Near Helford, Higher Trenower Farm. The farm has several properties and we stayed in Blackbird Cottage in 2009. The bed was superbly comfortable and the cottage very well equipped too.  http://www.holidaycottages.co.uk/cornwall/west-cornwall/blackbird-cottage

NO! The Studio, Manacaan near Helford. The king-size bed was two old single beds of different heights (!) pushed together and covered with a mattress topper - no support for my back!

YES! The Cottage at Kierfold house, Sandwick, Orkney: http://www.cottageguide.co.uk/kierfiold/ Very comfortable king sized bed. We stayed in 2010.