What should I use at night for an undergarment?

First, if it is a new occurrence to be leaking at night, I'd look into whether or not you have pouchitis. Leaking at night is one of my major indicators that pouchitis is occurring. If you've proven that is not an issue or still need extra protection, I don't have any real answers except to try putting a moisture protection pad under you while you sleep. I used one for several months after my j-pouch reconstruction surgery and it helped save washing my sheets daily.  As for garments, my Mom wears the Depends for Men and swears they work better for her than the women's. Just a thought.

I'm sorry you're going through this and wish I had better answers for you

I agree with Still Standing- definitely a sign of untreated Pouchitis. I also have used the Men’s Depends Underwear. I think it’s 19 per pack and I always have a stock at home in case they are needed.

I can try the Depends for Men.   I thought that might be an idea and have a new package of the ones for women to return anyway.  As far as pouchitis, I don't have any of the other symptoms, but I see the doctor in two weeks, so I'll see what she says. 

You don’t need to have the other symptoms for there to be some inflammation. That is how it starts. Nighttime incontinence. The other bad stuff comes later when it doesn’t get treated. That is what usually happens - Pouchitis gets out of hand when initial warning signs get ignored. It’s a huge red flag and if it doesn’t get better in the next 2 weeks it should be strongly suspected.