As France lost most of its colonies during the Seven Year war, your economy is essentially due to your own money production (taxes and Industry) and your commercial relations with other countries, however the Enlightenment had an impact on the low classes, they want to share the same destiny as USA, so if you want to stay under a French Monarchy the thing will be difficult cause if you decrease taxes, your economy will become a bottomless pit, so try to balance your economy and the happiness of your lower classes.

If you think that the Revolution is an easy way, let me tell that you're wrong, cause even if you wouldn't have difficulties with other countries under a Monarchy you will have some troubles to make them admitting your new regime and most of them will declare war to you, good luck. \nAlso you will be faced to other problems, the loyalists troops and black slaves wait to declare the civil war if you push too far the Republican idealism by the technology tree.

The challenge fighting under the Republicans or the king flags are equal, just find the way that you prefer.