The best way to overcome the urine problem is to buy a new mattress.
Go to How Clean is your House? With Kim & Aggie on Lifetime online and there is a tip where you take a small fingernail brush and brush a bar of soap. Brush with the stain, keep doing so and the stain will disappear. Take a towel that is damp stand on it on the mattress and go over the spot where the stain was to dry the area.