using oriental rug to make a cushion

I'm going to try to make a window seat cover from a very worn oriental
rug. I'm planning on cutting the best part of it. I welcome advise on
what to attach it for its underside; if it can be hand sewn ( I doubt
my machines could handle it); what kind of thread and needles to use;
seam allowances for the rug piece. The space it is going to occupy is
16 x 42 ". Any other advice?
Ellie