Which material is suitable?

Good evening, sorry for the long text!🫠

I'm currently building a camp bed like the one pictured above. I chose linen fabric.

After completing the frame and the lying surface, I unfortunately discovered that the fabric is not as instretchable as I first assumed.

So I sewed a thick canvas fabric made of 80% cotton underneath. This definitely helped. However, I'm apparently too heavy, and the fabric still stretches a lot around my upper body and hips, and unfortunately, it's starting to tear.

Now to my actual question: What fabric do you think would be suitable to withstand this much force without stretching or tearing? I want to re-sew the entire sleeping surface with the new fabric and, if possible, avoid a second layer of fabric to save weight!

Thank you in advance for your answers and I hope someone knows something about this!

PS: I had no idea about sewing or fabrics before. But everything's worked out so far, and I've been able to teach myself everything over the last few days. And sorry again for the incredibly long post!🫠😁