single seat from military versions ( ../A- models) or similar is the most comfortable place to stay on motorbike for hours and days.
This is my experience and the experience of several other MZ- pilots.
If you will get such a seat you can look for that in e-bay but they are not so often offered and you can not be really shure if the foam is still able for the requested cushioning.
(These seats as well have an age of 30 years an more)
If you need a special chassis for an single seat for TS I don t know.
For ETZ it is eiter necessary or you have to build something.
Concerning the requested price and availability you can think about other solutions like stronger cushioning.
But first: try riding a long and tiring day and look how it feels.
Position of footrest and position and form of the handlebar are as important as the type/ quality of the seat if you intend driving a lots of hours a day and lots of days in a row.
Pics of TS/A with singleseat
KLICK_01KLICK_02p.s.
in some travelogues the drivers swear on sitting most comfortable on lambskins.
