Not having a reference makes it a bit harder ^___^;
If you're doing a bulkier sort of horse, you can do it with padding to change the shape of your leg, like this tutorial
. While wearing a costume like this, your feet remain flat, and you can stand normally.
If you don't want the bulk, you'll want to do something more like hoofboots. Example on Deviantart
. You need strong legs to walk in those, and it's dangerous without practice x___x If you want the heel-less profile but a little more stability, you can bolt a plate to the bottom of the hoof that sticks out a few inches towards the back. This means you can rest weight on your heels without toppling over.