If I recall, the insulated piping serves two purposes: keep the innermost pipe surface hot to reduce creosote buildup and also to keep the exterior of the pipe cool to reduce burn/fire hazards. It might also help with draft. I would not put a single-walled stove pipe near canvas or wood. There's probably a standard somewhere about this. I'm sure some more experienced wood burners will comment.
Are you putting your wood stove in the center of the yurt or near the wall? If it's in the center, it can be pretty easy to send the chimney out the crown ring (unless it's a polymer dome). Otherwise I think there are heat-resistant silicone matts to patch into the canvas where the chimney has to exit that is commonly used. Or you could use a short section of double/triple-walled stove pipe near the canvas. Maybe.
As for
, memory foam would probably work. Basically, anything that is light & fluffy that can be put in place works as
, as long as it won't be eaten/lived in by critters or decay quickly (depending on your standards). If the price is right, why not? I'd also be tempted by rug pads/carpet underlayment.