Direct is OK. Our direct bids of Four, Six or Seven No Trump are standard. The Gerber ace asking convention can also be used if you like it. (We don't use Gerber).
1NT - P - 4NT = "15 - 16 HCP. "Bid 6 with a max, North . . . " or
1NT - P - 6NT = "I'm in charge - don't bid more" . . . or
1NT - P - 7NT = "Worlds fair here, North !"
Do Your Major Hunts It's usually advisable for responder to show his five card majors with Jacoby or ask for four card majors with Stayman sequences even though the intent is to bid a slam.
For example, 1NT - 2 © 2ª - 4NT can start a Blackwood sequence which shows 5 Spades on the way to Slam. Then someone may be able to bid 7 Spades over 6NT, assuming all the Aces.