ken,
there is a lot of research info out there, but typically it doesn't support the notion that the seats are the problem per se. Probably the most immediate improvement that can be made is to ensure the seat cushions are in good condition and properly padded - compressed cushions will lead to problems very quickly.
The overriding issue seems to be the posture that pilots are forced to adopt when seated, and several reports support that, though the effects of vibration are also considered relevant but there seems to be disagreement on the exact significance.
As someone who has had back problems for the last 20 years, I have some interest in this subject. I also happen to fly a modern type with high cost optional 'High Comfort Seats' that are probably the most uncomfortable seats I've ever flown in!
Anyway, I'm sure the following links will give you some food for thought:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA446461
Helicopter pilot back pain: a prelim... [Aviat Space Environ Med. 1984] - PubMed - NCBI
ftp://ftp.rta.nato.int/PubFullText/RTO/MP/RTO-MP-019/$MP-019-20.PDF
Back muscle EMG of helicopter pilots... [Aviat Space Environ Med. 2004] - PubMed - NCBI
Helicopter pilot back pain: a prelim... [Aviat Space Environ Med. 1984] - PubMed - NCBI