Hiya,
Try
http://www.visitscotland.com/ for ideas.
There are waterhouses available for rent at New lanark Heritage Site which I'm told are nice and the area is lovely. Not sure if they take dogs though.
Dumfries and Galloway is really nice too, and not so far up. There's a nice caravan site in Southerness and I'm sure they're fine with dogs. Great for fishing, lovely places to visit - Sweetheart Abbey is beautiful and lots of wee shops to provide your retail therapy.
For the ultimate in luxury and WOW factor look at this place
http://www.greatnorthlodges.co.uk/mountainbear.htmIt's expensive

It's in the Highlands, so quite a drive

But I HAD to show it to you.
One day, oh yes - one day I WILL have saved up enough money to go there !
Until then..............................................

Maybe I'm biased (being scottish, there's a good chance lol!) but wherever you go it's guarenteed to be beautiful, friendly and teeming with midgies !

The BEST solution for the midgies, by the way - tried and tested by the fishermen of my family - is Avon's Skin so Soft spray on body oil, it works a treat and doesn't stink like any of the commercial repellents - don't leave for Scotland without it - you have been warned! lol!