As Celia said
Posted by: pblanc on Sep-28-12 7:59 AM (EST)
you want to develop the habit of sitting with your torso upright maintaining some curvature (lordosis) in your lower back. That might not come naturally at first so I would stick with the stock outfitting first. Keep your initial outings short and focus on good posture. People tend to slouch more as they become fatigued.
That said, I know a number of individuals who could never get comfortable with the low seated position of a kayak and had persistent back pain. Those who still paddle have canoes now. Hopefully you won't be one of those.
If after a good trial use of your existing outfitting, you might consider padding your seat with a thin layer of foam to either cant your pelvis slightly forward or back. Stock molded seats cannot accommodate everybody's anatomy. If you do this, keep the foam thin so as to raise your center of gravity only minimally.