This video shows you how to make a cleaner to remove urine from a mattress. The ingredients in the DIY urine remover are baking soda, dawn dish washing detergent, and hydrogen peroxide. These 3 ingredients are readily available in most peoples homes, unfortunately, alone or combined they do very little to get rid of urine stains and odors on mattresses.
As a professional upholstery cleaner in Tampa FL I have cleaned hundreds of mattresses. Today's mattresses have synthetic tops and are easier to deal with then older silk top mattresses. That being said do not try to clean a silk mattress with the solution made in this video or any other water based cleaner it will only damage the mattress.
Removing urine from a mattress is a tricky thing to do. If you are fortunate enough to get to clean the mattress right after the urine has been deposited on it then you can get most of it out with simple water and a towel. If it's the next day and the urine has dried then your looking at a whole different ball game. Urine dries and forms urine crystals. These crystals, also known as salts, corrupt the soft fibers making them difficult to remove. If the urine has dried then a enzyme based cleaner is your best bet.
I can give credit to the video for showing the woman pouring the cleaning solution onto the mattress because the spray bottle would not get the cleaning solution deep enough to effect the urine.