In formal English it’s safest to use “yourself” only after having earlier in the same sentence used “you.” When the British reply to a query like ”How are you?” with “Fine, and yourself?” they are actually pointing back to the “you” in the query.

It used to be common to address someone in British English as “Your good self” and some people have continued this tradition by creating the word “goodself,” common especially in South Asia, but this is nonstandard.