It is great that you are thinking about your future health when considering donation.
you can discuss with your primary care physician and get his/her input. I know in Canada under a socialized medical system it may not be easy, but perhaps you can get in touch with a nephrologist to ask his/her opinion about donation given your medical history.
things to think about:
1. do you use NSAIDS (non steroidal anti inflammatories) in order to alleviate pain from your surgery of herniated disc. you will not be able to use them after donation or at least some opinions use them infrequently. this will be a factor
2. prior urological nerve damage. something to think about. perhaps ask your urologist about this. are you at increased risk with a lone kidney? are you at increased risk now or in the future for bladder infections. like you said, no need to have two people need a kidney.
3. in my experience reading so many stories from donors, it seems like transplant centers differ on their evaluation of kidney donors. There are no gold standards, each follows their own protocol, and as long as they follow the protocol they have established they are ok. so , will you get a truly unbiased evaluation? I have to say it depends. that is why I think it is good to get a second opinion for surgery, any surgery whether it is an elective procedure like this one or needed one.
4. this is the type of surgery that is planned so you should definitely take your time to think about it and educate yourself.
Keep us posted.
Best of luck to you and your intended recipient.
Sherri