Most back problems associated with sitting are relieved with a more open hip angle. There are several ways to accomplish that goal.
Often, the simplest solution is to raise the entire seat.
You can test out whether this will help by folding up towels or blankets or placing some pillows underneath you. This will open your hip angle without changing the seat angle.
The advice to raise your hips above your knees should be applied with great caution in a motor vehicle.
Car seats dip down in the buttock area in part for safety, to keep you from being thrown forward in a collision. In an office chair, hips-above-knees works. In a car, beware. You can use a seat wedge safely in a car seat, as long as it just lifts you out of the hole and does not entirely raise your hips higher than your knees.
If there is insufficient head room to raise yourself in the seat, it is unlikely any support insert will help.
How much head room do you have in the vehicle? How much space between the steering wheel/dashboard and your thighs?
The contour of the backrest should match as closely as possible, the shape of your spine when you are standing.
Spinal curves tend to collapse into a “C” shape when sitting, which will increase loads on the spine. Your backrest should support the normal “S” curve of the spine. Experiment with a rolled up towel or a small pillow placed behind your low back. NOTE: You must open the hip angle before a lumbar support can be effective. Lumbar supports generally don’t work if the hip angle is wrong.
Sit with your knees wide apart.
Lumbar spinal loads increase when you sit with knees together. Open your hips with knees apart and with some hip external rotation to lessen spinal loads and decrease back pain. Problem in a motor vehicle, is that it may be difficult to reach the foot pedals with the hips in ideal sitting alignment.
It is difficult to fit a car seat support via mail order.
If you live nearby, please call for an appointment. Fittings are free. If not, we recommend you seek out a back store in your community. Sometimes they have samples available to try out in your vehicle.