I'm planning to take the Trans-Siberian train from Moscow to Beijing, via Mongolia. We will start end of July probably.
We are still in early stage, so there are many questions and I hope you might help me here a bit:
Thanks in advance for your suggestions!
Book your tickets here http://www.trans-siberian.co.uk/our-trips/?gclid=CJmsleezzsMCFcZbfgodcRgApQ . I would say your standard economy class would be just fine. I had a friend who did this and thought his seating arrangement was just fine in economy class. I'm almost 90% sure that you won't be able to take another train if you get off your scheduled route. The website above has a pretty good FAQ page!