Ahhh, the Lakes District. After a recent visit, I fell in love like I knew I would - stunning natural beauty, clean air, beautiful lakes, great people (both locals and tons of visitors from all corners of England), hikes, and best of all...DOGS EVERYWHERE!
So much is written about southern England - London, Oxford, Cambridge, the Cotswolds, Bath, etc.. I had a tough time finding great intel about the Lakes District so I hope this helps you as you're planning.
We based ourselves in Keswick, which was the best choice after seeing all the other towns. I loved them but they can get very crowded. In Keswick, we were further from the main lures of the district like Beatrix Potter & William Wordsworth sites but it felt much more like an authentic, only in England feel. We met so many wonderful people here.
If you have very limited time, I'd recommend staying in Grasmere (The Red Lion has great deals) to be closer to all the sites. But I think 3-4 nights is really ideal to get a good handle on all the lakes and to feel the local rhythm.
In Keswick, Howe Keld is a dream B&B - great owners, fab breakfast (smoked salmon & scrambled eggs, local sausage, pancakes, etc), comfortable rooms, cozy beds, great value. I had a single room and my parents shared another room. I saw many of the more expensive hotels and I'd pick Howe Keld hands-down.
One of my favorite pubs I've found anywhere in the world was The Dog & Gun and we went every night. One couple had five border collies; another from Cambridge brought their dog eight weekends a year. We talked for a long time to Joe & Caroline, who had a white boxer and filled me in on their recent trip to Vietnam. Basically, EVERYONE we met was beyond friendly - exactly what you want in an English pub. Bonus: The food is great too! Nothing on the menu is fried but there are great soups, salads, and roasted deliciousness.
Nothing is very far in Keswick. A five-min walk leads you to the beautiful lake, Derwentwater, which I'm sure looks much different in the summer. There was something wonderfully atmospheric about being here in the off-season though.
The town itself is cute but not overly so - it hasn't been taken over by shops only for the visiting hordes. I saw kids skipping home from school, moms shopping with their babies, friends strolling around with coffees.
I'd highly recommend Bel Cibo for dinner one night while you're in town - we couldn't get into the so-called "best" Italian restaurant, Casa Bella, but stumbled upon this place instead. LOVED IT - cozy, great eats, and we met the most wonderful couple at the table over. They warned us about our next destination, Haworth, and I am kicking myself for not listening to them - but more to come on that disastrous night.
The Lakes District is a good five-hour car ride from London, but it goes by fast. You can take a train but you REALLY need a car when you're there.
If you're doing York, consider renting at Heathrow, driving to Lakes District, dropping car in York, then taking train back to London from there, which is what I did.
You will love it - I can't wait to go back!