Lumber, like a board bow is a good choice, but if you have made a few bows already, you could easily do a sapling bow like that. Cut a 2-3" elm tree, hickory, mulberry branch, plum, ash sapling or similar, and cut out the bow to like 95% finished. Handle as narrow and small as possible, limbs thinned to 5/8" thick or less, narrowed and tspered laterally, etc...clamp it down so it doesn't warp, and leave it in your house a couple or three days. Then move it to a warm dry place or your hotbox, for a couple more. Then, toast the belly, or at least heat it up a bit, to drive out the last bits, and tiller to brace height immediately.
I do this all the time for kids bows from about 40 lbs down, and generally small in dimension (56" long, 30 lb bow, etc...) if you are only, like 1.5" wide, and a little short, the finished thickness may be as little as 3/8", and that dries fast. This isn't the best way to treat bow wood, but it's about what Baker did when they built that paleo elm bow in a week in the TBB. I commonly dry a sapling stave in a couple weeks in the summer anyway, even for full sized, full strength bows, but I live in Utah, so humidity is rarely an issue.