Mortgage is in my name only. If/when I die, my housemate will be up a creek! I could pay off my mortgage using all the money in my IRA. Worth it for my peace of mind? --70+-year-old
YOUR peace of mind is only something that you know. However....
If you intend for your housemate to inherit your house, then you need to add them to the title/deed. Call your county and inquire as to what is needed to add someone to your title/deed.
You do not need to add them to your mortgage unless they intend to assume your mortgage when you pass. You should call your mortgage company and inquire as to what documents are needed to add someone to your mortgage or what would be needed in the event of your death for your housemate to assume your mortgage.