If you do some research, you'll find bamboo takes more set than any of the conventional bow woods used. Of course it isn't a wood, but regardless, I don't think it lends itself to a longterm short bow due to its issues with set. I think this is why the Yumi bow is so long, but I could be off on that. Do you know about heat-treating the belly of bamboo? If you do this, it will normally take considerably less set. You should research the best way to do this in advance so you don't just burn the fibres. I am curious why you want short and narrow. Short and wide is very comfortable to shoot due to its stability. For instance the paddle-bows of Pacific Northwestern tribes are very comfortable (albeit tricky) to shoot. You are obviously wanting to pull to full draw, but why not learn a short draw? It's fast and instinctive. Maybe not as accurate depending on your skill level. Last, if you laminate multiple layers of wood, The wood will generally be considerably more stable, meaning you can probably get away with a shorter design than you would with just one wood. Like the other guys said, Ipe and bamboo. Hell of a combo!