KimL, we took no buses in Vietnam. We flew and took the coastal train from Ho Chi Min City/Saigon towards Hanoi stopping for several days/week each in Nha Trang, Hoi An (loved it), and Hue (loved it), then flew from Hue to Hanoi. The train travel along the coast was scenic, albeit the train was old. We booked a quad with 2 bunkbeds, even tho we rode during the day. It was comfy to lay on the bed and watch the scenery go by with a few really scenic coastline areas. BUT, we were lucky with midweek rides and had no one else join our cabin. I heard weekends and local holidays are more crowded with locals visiting family. Another couple we met just booked the extra beds in their quad.
Not sure if you would be comfortable, as I assume anyone of either sex could end up.in your cabin. We chose the private rooms over a hard bench seat, but you could go that route and not take a chance on creepy cabin mates, esp for short stretches.
You will absolutely be fine flying. We used plenty of discount airlines with no problems whatsoever. We never took buses there, but met lots of backpackers who did, and some were women traveling alone.
We took several overnight buses in Thailand, and really liked them. We only took "1st class" buses there, which were just a few bucks more than regular. Lots of other westerners traveling and backpacking, and the seats were like business class seats on planes, but not lie flat. Lots of recline and a footrest. They even had a stewardess hand out snacks and water. Definitely nothing like greyhound, which I rode as a college student back in the day! If the long range buses are similar in Vietnam, you would be fine. I would bet they are better than the ones in India!
