My riding teacher has a horse like that, except it will run of with you if you don't keep its head down. We invented the Blue Thing. It's a small blue rope with clips on both ends that we attach to the saddle and run through his jaw strap. Works wonders!
Do more flat work. You. Need to become more supple through the back. Try more honches in or shoulder In. Do some counter canter. Because once the horse becomes truly round on the flat. The rest comes .💖
NEVER try to cover up issues with a gadget. they may mask the problem for a while but in the end the problem gets worse. go back to softening and suppleness. work on lots of stopping, direction changes, and transitions