Annie Sloan have a very soft easy to apply clear wax, buffed up it looks nice and performs as you would expect of wax. You can reallly go to town on it and buff, wax, buff wax for a good few coats.
Other options for tough coatings over chalk paint, Langlow Patina is much tougher than wax, it is “clear” but it will eventually yellow, being a polyurethane based gel. You can tint Patina with artists oil stainer or oil based paint and wipe that over the chalk paint and yellowing won’t be an issue.
In Cornwall, Plush Painting, uses the Colourman chalk paint and for extra durability they have recommended a lacquer over the chalk paint and then wax.
Other waxes and finishes over paint?