With disguise kit available to 1st level characters, maximum to 3rd level assassins or masterminds, and disguise self spell a 1st level spell, I think an illusionist or regular wizard should have no problem coming up with creating their own disguise other or general disguise spell by level 2 or 3 at DM's discretion. Without unbalancing anything.
I think there should be a general glamour spell covering people and things which lasts at least an hour. Even disguise self doesn't last long enough for a lot of purposes. Half our party with NPCs can disguise self, but we spent half the last week finding and doing a mission in order to commission a wizard to make a hat of disguise so we could run a scheme where he'll need to be disguised longer than an hour and we want to use magic, not the disguise kit.
While I can change colors of things with prestidigitation it seems odd I can't change the way things look for more than ten minutes until I get to sixth level and can use major illusion with its additional feature where it lasts until dispelled. I'm think there's room for improvement in 5e RAW illusion spells.