Dealing with incontinence, following a spinal cord injury,,,,,,, is it possible to get urine stains out of a mattress?

Slightly possible for a select few types of mattresses, but not very many, and not very likely. The best thing you can do is go to a mattress store and buy a waterproof mattress cover for under the bottom sheet. They're not expensive, and they're a lot better than stains.

It's not easy, especially with white mattresses for obvious reasons. There's one cleaner called Woolite Pet Oxygen that has done a pretty good job on mine; it's not sparkling clean like new but also not obviously a urine stain any more. Resolve Upholstery Cleaner also does an okay job at getting stains out, and smells significantly better than the Woolite. I use it on my wheelchair cushion when I need to.

I actually got one of those mattress covers that's supposedly waterproof; it hasn't worked perfectly for me, because the wetness does still seep through, but it's better than a regular cover. I supplement it by putting a couple of chux underneath it next to the mattress, and then sometimes also over the mattress cover and underneath my sheets (but usually only when I'm having major bladder problems because people can see them through my sheets and I want to avoid awkward questions...).

If you get a damp cloth and put it over the stain and run your iron over the stain it can help disguise or remove light stains. If that doesn't shift it, use some frend stain remover, put it on the stain, leave it for the recommended time and then put a wet towel over the stain and iron it using the steam shot of your iron. Just make sure you don't damage your mattress and make sure you follow the manufacturers instructions of the cleaner. If you have somewhere else to sleep overnight then you can use more water and put your electric blanket on top of it on high during the day or overnight to ensure it is dry. Perhaps even leave a dehumidifier in the room with it if you have one to make sure it is dry. Just don't leave the house with your blanket on.

I have found spray on/vacuum off carpet cleaner works too as does car upholstery cleaner. Once you have it as clean as possible, buy one of those waterproof not water resistant sheets and use it. I have woken up soaked in enough hotel or hospital beds to know some pretty good ideas to dry the sheets and mattress in an emergency.