There are non-breaking spaces, see:
http://www.w3schools.com.
But non breaking means non breaking, which means you could end up with very short sentences if someone decides to increase the print size.
I generally don't use super or sub script because if it is small enough to not affect the line spacing you can't read it. [1] are used by some people instead, though they are not as pretty. But if you have to do lots of footnotes, then it is not going to be too pretty anyway. You might use italics if they are not used otherwise in the text.