Practice riding without stirrups in a saddle first to build the necessary leg and core muscles.
Avoid "gripping" the horse with your knees, which can make you bounce. Instead, let your weight sink deep into your seat and follow the horse's motion.
Use fingers, butt plugs, or dildos with plenty of lube to slowly relax the sphincter muscles before intercourse.
Riding without a saddle requires significant balance and core strength as you rely solely on your seat and legs for stability.