You don't need any fancy stirrups in order to get your heels down! Just practice like crazy! The more and more you work on yourself to keep them down it will become muscle memory and you won't even have to think about it while you ride
Hi Bella, to teach my heels to stay down I stand up in the saddle and put all my weight in my heels, kind of like the two point but standing up more. This really strengthens my leg muscles too which would also help your heels. Do this a couple times a week continually and at all different paces then maybe you'll see a difference.