I have learned a lot about seats after building 5 custom rigid bikes.
I started working on bikes at age 16 and I am 66 now.
Still riding . (A rigid too!)
First thing to get straight is that if all you care about is how the seat looks on the bike
you may not ever be happy with the comfort.
Just like if you play guitar and you want the strings very low on the fret board.
You just will not get good results. The strings need room to vibrate.
A seat (any seat) must be level so that you are comfortable.
When you sit on the bike you should be able to just raise up your arms and the grips should be right there. You should not have to reach out to grab them.
It does not matter if you have forward controls or mid controls.
If the seat is tilted way up in front to "follow" the frame it will not be comfortable.
Any kind of non spring seat on a rigid is not going to be as comfortable as a spring seat.
No high tech foam combo will fix that. I tried. I spent hundreds.
The foam will help protect your spine from some of the damage though.
But the foam gets compressed over time.
SPRINGS-
The hairpin style springs are so stiff that they do not help much at all.
The cylindrical springs are very soft. For very light weight people.
IF you are around 200 lbs. the best springs are the behive style springs.
The 3 inch behive style springs are good for most people around 160-200 lbs.
Some of the 5 inch springs are good IF(very important) if they are heavy duty 5 inch springs. No wobble .
The springs no matter what height must not wobble from side to side.
The seat shocks seem like a good idea but should you have one or two of them? Seems like there is not much info available. I have not tried them so I cannot say.
The springs on the motorcycle seat are taking the place of the springs on your shocks IF YOU HAD THEM.
If you had the space for two regular rear shocks in your frame to attach to the seat they might be a good idea.
I have not seen it done.
The seat must be large enough to support you.
A 9 inch seat for a full grown person is not going to be very comfortable for very long at all.
A seat 10"-16 inches wide, and 13"-16 inches long will be comfortable.
I have found that a tractor seat metal seat pan is the best. It must be modified for motorcycle use. Narrower in the front.
Some of the tractor seat pans are better than others.
Some are very shallow and some are deeper.
If you need lower back support then the deeper dish seat is best.
The seat pans you se advertised on the web which is a flat plate bent up in the rear are
not going to be that comfortable.
Your body is not FLAT on the bottom.
It is a compound curve.
A modified tractor seat on a Rigid frame with 3 inch behive style springs.
Very comfortable even with out any padding.
The hinge of the spring solo seat must be as tight and precise as possible to eliminate any side to side play.