Brakeman, have a look at Sufoos' post from last week: viewtopic.php?f=44&t=12967&start=0
. He has rigged up a seat from a cut-down folding beach chair. It might give you the support you need. Also, have you tried different adjustments with the standard seat? If the tensioning straps are really loose, you end up in a semi-recumbent posture, which may or may not suit your back. On the other hand, if you tighten the straps and pull the back of the seat forward, it gives more lower back support. It really helps if you can stop the seat sliding forward due to the seat pegs slipping out.