Here's another vote for Peter Carney. He did for me traveling solo exactly what he did for others. I had some specifics in mind and left the rest up to him. He picked me up at my B&B (Ashcroft Guest House in Haltwhistle) in the morning and returned me there at the end of the day. Peter is both knowledgeable and charming. I learned so much in such a relaxed and pleasant way. I can highly recommend him.
Below I'm telling you more about where I stayed because it was one of my favorite places on a 6-week trip to the UK. When I was there in May 2016, there were very few people around. Perfect.
My room was the Single En-suite. The same room for 2 is called Smaller Double En-suite. The website shows pricing for the various rooms based on occupancy, so there are multiple listings of the same room at different prices. I stayed there 2 nights with the full day between devoted entirely to Hadrian's Wall.
Haltwhistle is tiny. You can easily walk to the Ashcroft from the train station. You can also easily walk to get something to eat.
When it was time for me to leave, the owner drove me to the station because the platform is on the other side of the tracks and it's not obvious how to get there. He stayed with me until the train came and we had a great discussion about our kids.