
I think the Dogs Trust has a bit for holidaying with your dog in cottages and I think the charity get a percentage of the rental fees if you book up. Have a look on Dogs Trust website.
I book cottages in Scotland all the time for holidays with Copper and you need to watch because some places do allow dogs but charge extra. I use Mackays Agency and the places I have used have been great and very reasonable but they only do Scotland and North of England.
Have a look at both of these. Hope you find something!
CG