I tried reversing the headrest in my Model 3, but it felt super unsafe because of how far back it was. I tried all sorts of pillows and cushions and eventually found a solution that works for me. I took a 12x12 inch piece of 1/2 inch thick memory foam and added it inside the seat. Picture is below.
This does two things, it makes the upper back portion of the seat slightly less concave, and it pushes your upper back slightly forward away from the headrest.
I'm still not crazy about the comfort of the seat, but it's comfortable enough. This is the only solution I've found that allows me to drive without thinking about seat comfort.
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