FIL is nearing 90, and is always cold! He has the heating on pretty much 24 hours a day plus a little plug in one that blows hot air out. He used to have an electric blanket but it stopped working and we never replaced. He wants another one so he can reduce the bill but the thing is he sometimes pees the bed, if we put a matress protector and waterproof sheet over the top of it will it be safe?