I would also pick England as a first trip. There are enough things similar to the US that it's not that much of a culture shock. If you don't like a big city, you can take trips outside of London fairly easily.
My first trip was in 1968 and at that time an economy seat was plenty of room for me. I went alone but stayed with a friend. Since then I was in Scotland several times while in the Navy and managed to get a couple days off to go to London. This was in the mid- 70s. My wife and I have managed to get to London almost every year since about 1999. (Thanks MP and HHonors!)