Free vs Premium doesn't effect welfare index. A high welfare index is better than a low one. However, countries with high wages will benefit more from having a high welfare index. Since Welfare Index and Wages interact to increase Corporation productivity, you need both high corporation wages, and high welfare index, to see the full benefit.
If you want to know how to increase welfare index, the documention provides the answer...
"The Welfare Index is the lowest value of several other indexes:
The Health Index
The Education Index
The Transportation Index
The Supply Index + 41
The Employment Index + 37
The Social Security Index + 38
The Government Salary Index + 27
The Consumption Index contributes between 0 and 8 point to the welfare index. It needs to be at a level of about 300, to reach the max effect."
Note that the 0-8 from the consumption index is subtracted fr