Jeff - A picture or three would speak volumes so we can try to understand your problem.
Perhaps you can post some pictures showing the existing and potential replacement door latches, plus the "lock knob" you mention.
On a slightly different thought, what's wrong with the existing "latch" making it necessary to replace??? The latches do have some parts that can be replaced to restore certain functions, but since we don't know what's wrong with it, we cant offer the best help possible.
