"Horse bow" is a pretty open-ended description (even more than 'longbow'). It covers everything from Hun/Magyar to Persian to Ottoman to Mongol to Manchu -- and everything in between! All different, but all of them bow styles used by nomadic and military horse-mounted archers.
For a one-time laminated bow I would suggest a simple 2x12 and rubber band form like mine in the picture below. To cut out the curved shape you DO need a bandsaw -- a sabersaw will
NOT work DAMHIK. The rest of the form is 1/4" dowels and rubber bands you cut from a free discarded bicycle balloon tire innertube.
If you message me your address I'll send you a tracing of my Scythian style bow, shown below, along with the total thickness of laminations of wood and fiberglass you'll need to buy to get that 45# @ 27". I'll also send along the step by step instructions for building the bow. Binghams has all the laminations you need, plus the Pint Kit of Smooth-On EA-40 -- the epoxy of choice.
48" tip-to-tip, mine is 35#@28"
FYI -- I'm going to be out at sea and out of internet range from the 25th through the 30th...