The issue you're going to have with this question is that "severity of repression" is very subjective. Libertarians, Conservatives, and Social Liberals all have very different views of what kinds of behaviors are oppressive, and what kinds of oppressions are the worst.
Normally, that would mean this would be an off-topic question here, asking for opinions, unless some researcher has actually done and published this analysis so we can just point to that. Fortunately, someone has. In particular I found this dataset from Wikipedia's list of freedom indexes, that looks like it probably covers the years and countries involved:
MaxRange, developed by Max Rånge, and maintained by Mikael Sandberg
and Max Rånge, political scientists at Halmstad University, Sweden, is
a data set defining a country's level of democracy and institutional
structure (regime-type) on a 1000-point graded scale. Values are
sorted based on level of democracy and political accountability.
MaxRange defines the value corresponding to all states every month
from 1789 to the present.
Unfortunately, it doesn't appear to be online (anymore), so one might need to go to the authors or Halmstag University to get access to it. Here's a Wayback link to its website, but none of the data links there seem to work for me.
There also is the Polity Data Series, which goes back to 1800, so it also ought to cover the period in question. It was sponsored by the CIA, so it makes some rather myopic choices (eg: giving the USA a 9/10 during freaking slavery), but it may be a good counterpoint to the Swedish one. Probably easier to get as well.