Next time you're out, reverse those pressures front and rear and see what it does for the comfort on the roads you described.
A stiffer rear will give any car a "flatter" ride with less pitch sensitivity at low frequencies like potholes and speedbumps. Pitch is particularly uncomfortable so you want to reduce this.
Try to ignore handling so don't rag it or let this convolute the issue, your car might handle worse or whatever but the hope is that by making such an extreme change to tyre pressure you might actually notice something (or... you might not). Then you can change it back, but at least we will have some feedback from you on how this worked.
Honestly I haven't looked yet, what does it say on the passenger door for tyre pressure?