Want information about 30-year lease or register a usufruct

We're not married, been living defacto for past 13 years in a very close loving relationship. We live in my Thai partner's home in rural Korat. She owns the land, and house, all in her name. She's never been married, doesn't have any children. She made a will a few years ago at the local amphur which states that her sister's 2 daughters will inherit her property.

She's nearly 60, I'm in my late 70s, so in all likelihood I'll pass away before her. But, in the event that she passed before me (which I hope to God doesn't happen) I would like to legally remain living in this house for as long as I so desired, which at my age would not be such a long time. I wouldn't want her family to turf me out so they can get their hands on the property, I know wills and inheritances can bring out the worse in some people.

So what is the easiest way for my partner to make some arrangement so that in the event of her passing before me, I can legally remain living in this house?