I was informed by some people that only KJV is the perfect bible
You should probably separate yourself from the KJO (King James Onlyists) cultists. They have made an idol of a particular translation.
The KJO isn't "perfect". Our confession teaches us, "The Old Testament in Hebrew (which was the native language of the people of God of old), and the New Testament in Greek (which, at the time of the writing of it, was most generally known to the nations), being immediately inspired by God, and, by His singular care and providence, kept pure in all ages, are therefore authentical".
As for translations, " But, because these original tongues are not known to all the people of God, who have right unto, and interest in the Scriptures, and are commanded, in the fear of God, to read and search them, therefore they are to be translated in to the vulgar language of every nation unto which they come"
So, if you are teaching folks who are experts in Early Modern English (Shakespearean scholars, perhaps), then the KJV might be the translation of choice. But it certainly isn't in the vulgar language of most of us these days.
For debates as to manuscript families, see earlier threads throughout the PB. But that is a separate, if overlapping, issue.