No ones answered so I will offer my advise,
Don't do it unless, you have a drying fascility, a memory foam mattres or tempura which can cost a couple of grand absorb tons of moisture as the name suggest... FOAM.
It will take 5 days to dry in good conditions, and of course it will weigh a ton when wet.
The way to clean is to soak the area until the moisture is coming out the back taking the contaminants with it, as you can imagine this takes a long while and the mattress has to be supported on a frame to allow air movement.
Some people use hydrogen peroxide which will discolour the foam but works effectively in removing the urine.You can also pop along to your local pet store and get some pet urine remover, same method.
I once heard of a guy who soaked one then applied detergent :
took him a week to get the suds out alone.