I have the place for you.
The Low Wood hotel, see web site here:
http://www.elh.co.uk/hotels/lowwood/index.php
My family had a Christmas break their this last Christmas and it was lovely.
As you can see from the picture, it is right on the shore of Lake Windermere. You can walk from the hotel to the lake in about 30 seconds.
It is isolated, but is between the towns of Ambleside and Windermere, which are about 2 miles away (in opposite directions, Ambleside is North and Windermere town is South).
As you can see from the picture, there are hills behind and the footpath up the hill is right behind the hotel.
There is a swimming complex alongside the hotel, picture here:
http://www.elh.co.uk/hotels/lowwood/caption.ph p?id=379
Some rooms in the original part of the hotel do overlook the lake, and I think one of the rooms has a 4 poster bed.
There is a modern part of the hotel but this is at the back of the hotel and does not overlook the lake.
Food was excellent.
This is the view from the breakfat room & dining room, as you can see, you can see the lake from the window.
http://www.elh.co.uk/hotels/lowwood/caption.ph p?id=395
We had three days there over Xmas (it was our daughters 21st birthday on Xmas day) and we did not have a single complaint.