a bright saddle pad and polos. maybe a vest. many people sell vests used for riding in the roads so cars and stuff see you. Also you can find bright and reflective gear used for riding in woods or trails to avoid hunters
I would recommend buying reflective boots for your horse, a reflective browband, and a reflective decal for your helmet. If you want to be extra safe, you can also use a bright coloured saddle pad and jacket for yourself.
Hope this helps! :)