The Flyer is the same as a B17, but it has springs in the rear. But before you run out and buy one, the springs are very stiff. I use a Conquest which has the same springs as the B17, when I put my weight on the saddle it only depresses the springs maybe 5mm, so you are not getting a much smoother ride. I think they are best on a rough pavement like chip seal that can give you almost a vibration type of ride. So, if you are on a smooth road, I think the springs on a Flyer would not feel any different than what you already have.

I know nothing about the B66.

I wonder if a suspension seatpost might work better? Sometimes I use a cheap telescoping type one on gravel, the one I use is like the cheap ones that are common on some hybrids, but it does not do much.

These might work better: They are similar to the Thudbuster. But I have never used one like these.