A Single Word For Person without any bad habits
Solution 1:
An informal single word as asked for could be, as Lexico gives, a
saint
NOUN2 informal A very virtuous, kind, or patient person.
As a phrase, the person could be called a paragon of virtue. Lexico says
paragon
NOUN1 A person or thing regarded as a perfect example of a particular quality.
it would have taken a paragon of virtue not to feel viciously jealous
The Lexico entry for virtue is
virtue
NOUN1 Behaviour showing high moral standards.
The man was one of great virtue, and his morals were admired by everyone.