I previously posted asking for help with solutions to getting enough headroom in the car to drive on track comfortably in a helmet. I did ultimately solve my issue and I'm posting it here for posterity (and the guy who asked for details in that thread). I cannot find any lower options besides maybe doing side mount seats directly on the ground. Godspeed and good luck if this helps you.
Parts:
Skillard Seat Mounting Brackets (Driver side)
Corbeau Seat Bracket (Passenger)
Corbeau Sportline RRS Seats (A4s should fit as well, minimal padding is key)
Braum Racing 370 Harness Bar (you will lose the passenger stock seatbelt)
***Braum 4 point racing harness (2x)
Braum Universal Harness Mounting Bracket Long (2x)
Braum Universal Harness Mounting Bracket Short (2x)
Airbag light spoofing plug (haven't purchased one yet but that or some messing with resisters and wires is necessary to drop the airbag light)
I had to do some bullshit with the harness mounting brackets. I think I had to fab my own piece to mount the harness to the back right bolt securely, but I didn't have time to remove the seat to validate with photos so you'll have to get creative when you get in there to get all 4 points to mount properly. The passenger side is easy. if you just like the setup and don't need the headroom you could run corbeau seat brackets on both sides and I believe this would allow you to retain your seatbelts. I didn't remove mine from the car in case things didn't work out but I'd recommend dropping yours for a maximally clean look.
***Edit: After several commenters informed me of the risks of a 4 point on the street I'm looking to a new breakaway style 4 point, currently looking at the Schroth Professional II-FE.