there is a difference between Eu só/ Só eu tenho and só uma perna/ uma perna só. In English?
"Eu só tenho uma perna/uma perna só" = I only have one leg
"Só eu tenho uma pena/uma perna só" = Only I (and nobody else) have one leg.
In English, you could say either "I only have one" or "I have only one" - both are correct and have the same meaning. For the second phrase, both would normally translate to "Only one leg".
Does that answer your question?
Memories of a Peter Cook / Dudley Moore sketch about a one-legged actor applying for the part of Tarzan and being gently? refused ("I have nothing against that leg but unfortunately neither do you")