Had discectomy last summer (l4-5), and after about 5-6 weeks I was riding mtb, road & hybrid bikes. Had to take it easy, but no issues whatsoever. After 6 months I was snowboarding. This season I don't even think about it.
For mtb, I'd certainly go full suspension. It's just better even if your back is fine. Skip the WSD and just get a smaller size if necessary. Stay away from the brands that set up their bikes with longer top tubes, or just get the next size down. Also stay away from agressive XC racing geometry, like the Epic. Just not comfortable for long rides (similar to racing road bikes). I found that the Stumpjumper FSR is exceedingly comfortable for long rides. My stance is more laid back and upright.