Driver's seat trunk support?

I just got a new car! 

Here's the issue I'm having. I currently transfer into the driver's seat to drive. Whenever I make a sharp-ish turn I have a tough time stabilizing myself and I find that I'm leaning on the steering wheel for support. I've got a chest strap on the seat right now, but it's not doing enough. 

Back in the day I had lateral supports on my wheelchair like these. Has anyone Macgyvered a way to attach these to their car seats? Or does anyone have any other mods they've come up with? 

Thanks in advance! 

--SD