No probs to find a bedspace in a hostel around Kao San Road area, there are so many around.
However there are favorites and it could pay off making a reservation for those as those popular places are often full.
Hostelworld is a better place to find out about those.
There are plenty of inexpensive guestshouses around, too, and without doubt you will be told that those is a better, more traditional form of tourist accommodation.
I recommend to stay away from them, too many old travelers there who tell you what you should do, and how much better it was in their time, it's boring and annoying.
My opinion only of course, others see it differently.
One way ticket can be a problem when boarding the plane or applying for a visa. You might get into troubles there. Look around the forum a bit, this topic is all over the place.
