I bought one of these on the recommendation of my chiro. It has been a miracle! My lower back / sciatic / sacrum problems are gone. Takes some getting used to because it keeps your pelvis from rolling under like it normally does as we hunch over. Less than $15 goes right on the seat you are using now.

http://www.amazon.com/gp/aw/d/B007LX...sr=8-2&pi=SL75