I double track a lot of vocal tracks. Sometimes even up to 6 on background Vox.
Key is to be precise in singing it. I've met people who are masters at it. Not to toot my own horn but ive been doing it for 30 years, back when it was 3 tracks for vocals on an analog 8 track reel.
Freddy Mercury was one who was almost perfect. mind you this was the days before digital audio. You need to look no further than Bohemian rhapsody. Its a great example.
Before you hit Melodyne use Vocal synch to tighten up small parts.
I find Vocal synch to be cumbersome but if used lightly, you can get away with small lifting (without artifacts) and use Melodyne for the heavy lifting.