I know all about lower back pain; and the worse part about any pain in general is not having anyone to relate to. So I feel for ya, Paul.
Those large work-out rubber balls are really good for back issues - but you really need to spend time on them (10-20 min, at least a few times each day), stretching and doing various movements, roll over them back and forth, place your hands on the ground and roll your shins over the ball so you get into a folded kneeling position with your upper body folded over your thighs like they do in India or wherever it is; then go backwards until you are (nearly) balanced over your stomach on top of the ball, squishing it; it should always be a flowing movement and not abrupt or block-like movements; but even just merely rolling over onto them with your stomach feels great and it really stretches the back if you do it right (have a couple of strong woofers pull hard on your legs and arms while you are on it after you have stretched on it a while, before getting off and the G force (gravity - a theory, folks!) compresses your back again - I would get two of them if I were a giant.
Apart from those big squishy rubber balls, the BEST stretch I do is to stretch from side to side. Stand strait with feet at shoulders' length apart, stretch your arms upwards while keeping your stance, then visualize the side-to-side plane as though you were butcher slicing through your own body with a giant cheese slicer cutting your body right in half so that you have the front half and the back half - now bend exactly sideways within that plane, over one leg (the other leg can lift off the ground a bit to help you balance out) - SLOWLY - so that your arms slowly move like the hands of a clock from noon to 5PM-6PM (if you can). The leg that you bend over ought to be straight so that the only main pivot point is really your hip bone. Visualize each vertebrae stretching the spinal cartilage so that each side of your vertebrae opens up the opposite side that you stretch towards, starting at your sacrum, lumbar vertebrae etc. right up to your head where by this time your head/arms should be at 5PM. Then - SLOWLY - bend back up in reverse, but again visually starting with your sacrum. Then to the other side. Do this maybe ten times each side, a few times each day. It takes time to do; each side should take you 2-5 minutes - longer if you're really into it. You'll see how you will feel after just one complete stretch - don't try too much at a time. After a few times you should start to really feel AMAZING right after each stretch, if not then it is not the right stretch for you. IF IT IS EASY YOU ARE DOING IT WRONG.
Another thing, besides spas and being in the water, swimming hard, or just floating there for an hour like a dead carcass... is to get yourself a workhorse and a few pillows, place it legs' length away from a railing or picnic table, then bend over it with your stomach over the padding/pillows located on the top of the horse while placing your heels (wear boots) under the railing or picnic table and slowly straiten your back out with all of your weight mostly between the top of your hips and stomach (feel around for a good spot; you should be able to balance your body over that spot) on top of the horse (I recommend a steel horse for you, Paul; make sure it's not a rusty old thing that will break in half and stab you in the torso before hitting ground). Try sets of 5-10 at first bending down over the horse - SLOWLY - with your arms extended, hang there a while, then flex backwards back up strait (horizontally); do that a few times a day with a little opium and you should be fine.
PS - If y'all are wondering why I edit stuff so much it is because the NSA is cyber harassing my grammar and changing things like "do" to "to", "knowing" to "nowing", "mutt" to "butt", "where" to "here"... but, hopefully I am just paranoid.