3) Change your posture - remember to move your posture from time to time. Wait until driving conditions are suitable to allow you to wriggle in the seat to alleviate postural fatigue.
4) Take breaks - driving is tiring work and to avoid driver fatigue and minimize postural discomfort it is good take to fairly frequent rest breaks that allow you to stand up and move around.
5) Seat accessories - you can choose a variety of car seat accessories that may improve seat comfort for you, from fleece covers to soften the seat to bead backrests to provide for some kind of back massage while you drive. Choose whatever you find adds to your driving comfort.