Have the French create a multi-cultural Super-Lebanon which includes OTL Lebanon, the coastal region of OTL Syria to OTL Lebanon's North, and the region around Damascus. On the other side, have the British retain Shi'a majority Mesopotamia. And either have an independent Kurdistan, or have either the Turks of the Persians in control over that region.
The area in-between all that is roughly similar to what ISIS held at its zenith, and would just be a run-of-the-mill Sunni-majority state. Being land-locked, it may end up being pretty reliant on the good will of the neighbours. The obvious potential 'best friend' is Jordan, and the best way to do that is to have a relative of the King of Jordan on the throne of this country ("Syraq"?).
Although there's always potential for religious radicals staging a revolution, the very fact that your sea access relies on the good will of the monarch next door, who is a relative of your own monarch, entails that it's unwise to depose your monarch. It would be a bad move, economically. Religious nuts may not care, but plenty of fence-sitters will side with the King's existing government (even if they don't like him) out of practical considerations.