There are saddles that are split in the back to take all pressure off the tailbone area. I ride with a gal who injured her tailbone badly in a bike accident years ago, and she needs this type of saddle.
Here's just one example:
http://ridingbicycles.com/itemdetails.cfm?LibId=29722
Warning, tho, a lot of these saddles cost more than the bike you are are currently riding!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow