JonT,
I also have a disk bulge at L5/S1. This is my second major episode of sciatica and I can definately understand the situation. I am a nurse and if I am unable to resolve this problem without exercise, I will be unable to pursue my career (which I am VERY passionate about).
What I'll say first is surgery is ALWAYS a final option. The trauma of surgery (especially when it's not necessary) can sometimes make matters worse.
At first, once the cause has been found, it is best to go to your GP and get a referral to see an exercise physiologist or physiotherapist. They have the knowledge to be able to set out an exercise regime that will SLOWLY build up the strength in your back. The key is doing it slowly, and by seeing a professional they are able to instruct you on the exact way an exercise should be performed. (The pool is a great place to stretch and exercise because it takes the weight off your spine and allows for more comfortable movement.)
A big thing to remember is to NEVER go past the point of pain. As soon as you feel any twinge of pain, stop - return to a "neutral position" and rest. You are the best judge of your body and how it feels, so be aware of your body (its alignment and action of the muscles) and don't over do it!
You might find "back flexion" to be of some help if you have a bulged disk. But again, be very aware of the pain you feel during this - only go as far as you feel comfortable. If it doesn't feel right, it probably isn't so stop. Just google back flexion and you'll be right. Start off doing 1 set of 10 reps daily (1 rep every 5-6 seconds). At first, you might feel an aching sensation in your lumbar/sacral area, however this should settle. Back flexion works by manipulating the bulging disk back into its proper place.
Good luck with everything mate. And ALWAYS get a second opinion, even a third.
Take care.