Or even fully embrace slavery to have more labor for factories and let slaves handle all the poorly paid resource gathering. Going all the way to slavetrader too.
Naturally all combined with the freeest society ever.. for nonslaves. Oh and colonising africa would be a good idea for the purpose of surrounding some high pop area as a eternal slavetrading source of slaves. Americas own little HEART OF DARKNESS in say kongo.
Meanwhile everyone free can enjoy middle living standards (30+?) as a minimum. Strutt about with twice the SoL of the next highest.
Now that is a real motivator to study the stem stuff for engineering, even study religion, wouldnt want to be stuck working with slaves in the mines? Even if a freemans pay would be much higher.
That's not likely to work well.
For one, assuming slaves don't dramatically improve economic efficiency apart from their own meager wage (well, meaning cost-of-living since it's "paid" in board and lodging) the extra wealth to be divvied among the free population is simply not that great. They do almost-free work, don't lay golden eggs. The more slaves you have in proportion to your free population, the more wealth of them can get, but there are likely to be certain dangers associated with pronounced minority rule over an enslaved majority.
Second, this would screw over your labor sector. Untrained workers can't compete with free slavers, so they need to get educated en masse – which itself is expensive for your country to provide – and would likely suffer lower wages due to the increased competition in the trained professions available. Furthermore, the education has a nasty way of making your pops into free thinkers who will eventually make it harder to maintain slavery, though that's probably something you can offset via other means for a while at least (eg. improving standards of living, if you can manage that). Since enslaved pops use only few goods, your economy will likely feature cheaper luxuries, which will offset some of the gains to the factory owners for the costs saved by employing slaves.
To offset some of the problems caused to your free citizens for the adverse labor conditions created by the competition from essentially free slaves, you could of course try to create a progressive tax code that re-distributes the "excess wealth" created by the slaves more equitably to the populace, not just the owners of the factories and plantations, but generally the fat-cat elite who own the slaves are not particularly prone to supporting dramatic redistribution of their own wealth.
EDIT: Forgot to mention but the increasing tech as the game progresses is likely to render the gains from slavery more and more meager as work becomes more automated, less labor-heavy. A slave economy might be able to compete against manual farm labor and all that, but ultimately who needs a thousand people in a chain gang when you can buy a couple of tractors? Then you're left with the costs and political repercussions of maintaining slavery, with ever-marginalizing benefits.