Lark, rather than picking a purebreed dog, what about a mixed breed? I strongly suggest adopting rather than buying. Most of the dogs I've had found me rather than me seeking them out. The few times I adopted I went to my local animal shelter and walked through looking at the dogs available. Both times the dog picked me.
A couple of suggestions for learning about breeds, visit your local library. They should have books on various breeds and their characteristics. Online try googling something like "small dog breed characteristics."