I've been riding a full-suspension mountain bike exclusively since 2002, and I also have herniated lumbar discs (3 of them). I'm 6'1", 230, and car-free; under VA care, so you know it's not Johns Hopkins.
What has worked well for me is to have the forward-leaning position, bars about 1" below saddle height, and top-tube length somewhat less than the XC guys would recommend.
That said, remember one thing: 2mm of stem height change can make all the diff in the world for your own ride, so don't be afraid to experiment a bit. Also, make sure your cadence is up more, less mashing -- 80+ rpm on the pedals keeps my low back from seizing up.
Hope this all helps.