Have you considered a geodesic dome kit? you can order them custom made or by pre-existing plans. You can get them any size, you can get them high or low (no stairs you mentioned.). You can get multiple domes joined together. Domes are hurricane and earthquake resistant. Many companies offer struts made of wood or metal. Obviously choose metal if you are seriously concerned about fire. You can buy everything you need and have it delivered in a truck and assembled in a matter of days.
I personally prefer wood, and am less concerned about fire since I live on the west coast in a wet climate. I would love to be able to build a geodesic dome from Natural spaces. They have designed the dome so that even as the dome increases in size, the struts are still smaller and there are more triangles. It's easy for anyone to lift, although I don't know what condition you have or how debilitating it is, but you may even be able to help in the assembly to some degree, or find friends to help. They are designed to be built by owners easily, but you can also hire a crew to erect it for you.
My plan for a geodesic dome made from wooden struts and plywood sheathing was to finish the interior with lime plaster or lime wash. lime offers a certain level of fire resistance. plus it looks nice. I haven't figured out if you can berm a geodesic dome yet, but that would certainly add to it's stability and thermal efficiency.
Perhaps I'll need to start a thread about geodesic domes to get some input about these questions, but to me it sounds like your best option as far as being affordable, disaster proof, and easily built, also quickly built. Here is the link for natural spaces domes, there are many other companies, just search for geodesic dome kits. http://www.naturalspacesdomes.com/