Recaro Seats makes a base, or at least used to for the automobile seats.
Recaro is the OEM manufacturer of seats for Mercedes and Porsche, to name a few.
I have an aftermarket seat in my office. It isn't powered by it is very comfortable. The base allows for tilt, height adjustment etc.
You may want to start here: http://www.recaro-nao.com/
Keep us posted,