go with the flow ! (of the horse's trot)
Drop your sturps take your leg and pull it behind you while you slightly move back . Do it to both legs for 10 seconds 5 or 6 times and it will relax your hips
just let those hips move like beyoncé
Try riding with no stirrups. Will help because your leg is longer. Or you can lengthen your stirrups a little. Sitting is a lot easier with a longer leg.
Riding without stirrups helped me when I was learning. Also doing lots of stretches to open your hips.