We've just stayed in one of the houses from Niche Retreats and it was fantastic and far removed from the chintz that can be Cornish self catering.
We stayed at The Boat House which is about 30ft from the sea so a fabulous view of pounding surf in the evenings and early mornings is followed by a practically empty beach and rockpools by lunchtime. They provided fluffy towels, duck down duvets/cushions and soft pillows plus they unpacked our Tesco.com order so it was all put away by the time we got there. There was also a huge bunch of flowers on the table and a bottle of wine, a corkscrew and 2 glasses waiting for us. It's warm and double glazed so you can shut the sea out if you want to. There are 2 bedrooms, a twin and a double, plus 2 bathrooms and 2 loos. There's room for a travel cot in the twin room too, and they provide all bedding.
We found starfish and crabs and mussels (we picked them and cooked them, which fascinated the children) on the beach and just had a fab time, I'd really recommend it for an old fashioned but peaceful family holiday. No mobile signal so it really was getting away from it all, bliss. I'm almost reluctant to recommend it in case mumsnetters book it and I can never get in there again but hey, the greater good and all that, I thought you ought to know