@Exutant - I totally understand why you cleaned the sheets.
This happened to me once, and it was the bed we were both sleeping in.
The (not then) husband was still so drunk, he just got up and moved to the spare room and fell straight back asleep again because still drunk, leaving me to sort out our bed.
Of course I did it because otherwise it wouldn't have been done, and he would NOT have done it.
But it was only once. I told him if it ever happened again, we would be over. It never has, and in fact he stopped drinking for a long while shortly after that. He doesn't drink much at all these days - and mostly his "sessions" are when he's away with colleagues, and they go out after dinner, so he's in a hotel. No idea if it's happened there!
I know how much hard work it is to clean up piss from a bed - and I know full well that the only way to ensure it's done even remotely properly is to do it yourself, unless you have a partner/husband who actually gives a flying fuck about things like that (amazingly, some do!)
I agree though that he is treating you very badly. And I would tell him that HE is paying for the mattress himself, as HE trashed it and it's the bed that HIS mother sleeps in, so unless he wants his mother to sleep on a mattress that he ruined with his drunken pissing, he'd better cough up.
Having said that, it's pretty wrong that you only get "housekeeping" from him as a SAHM and you're expected to pay for everything out of that! Sounds like there's some financial abuse going on - a city lawyer is probably on near 6 figures, if not actually 6 figures, and can certainly afford a new mattress!! Why do you not have a joint account? Time to talk about that as well in your marriage counselling, I think!
I am a SAHM too, and I do get money put into an account for me every month BUT I also have access to the joint account. My savings account is for buying things that I don't necessarily want the husband to know the cost of, like presents etc.
I need to have access to the joint account for paying bills and in case anything happens to DH while he's driving around (have had a few friends who've lost their husbands to car crashes etc. :( ) - what would happen to your finances if your DH suddenly died?
His flippancy over the mattress and his behaviour is the most repulsive part of this episode though. At least my DH was mortified about it when he woke up in the morning, and took steps to avoid it happening again - yours seems to accept it as part of life and your duty to clean up for him. This is Not Acceptable. Not good for the kids to see him abusing you like this either (emotionally/financially).
Hope you can resolve this in a way that works best for you. 