Right now, it is possible to make an employee 100% satisfied, by making sure you meet the requirements regarding working hours, and some have requirements for a sofa, coffee machine, etc.
In my view, it is too “cheap” - based on the above, I think it should only be possible to get an employee up to 90% satisfaction.
Next, the last 10% can be allocated in 2 areas:
Union (price per employee)
Registering the individual company to a union must give 5% happiness.
The cost can, for example, be 5 dollars per day per employee - but in addition to 5% more joy, it must also give a discount when they are trained (skills)
Health insurance (price per employee)
Enrollment of the individual employee for health insurance must also give 5% satisfaction.
the price could, for example, be 5 dollars per day per employee
At the same time, this could also provide the opportunity for some new achievements.
Such as the number of employees who have Union or health insurance, or it could be measured by how much money you had invested in this - to take care of your employees.