Scots offers 'youse' as another effective second-person plural (this has also become common in
Australian vernacular in recent decades).
There is no modern-sounding English pronoun that is unambiguously singular, but the archaic
(some Northern English dialects preserved this usage up to the 1950s) 'thee' and accusative
'thou' will do, if you don't mind sounding vaguely biblical.
If you do use these, please please conjugate your funny old verb forms (thou dost, she doth)