I'm assuming you're doing some long range planning here, because the SXM airport is closed right now! You could take a quick ferry ride to Anguilla, which has gorgeous beaches and a low key pace. We've done several catamaran day trips there and have thought about adding a few days' stay. Other places people fly or ferry to are Saba and St. Barts, although those ferry rides can be rough and not for those prone to seasickness. While I've not been, Saba is very different, with few beaches, although good diving from what I've heard.