When looking for horse riding boots for flat feet, what you want is a boot that will support your arch. Though you do not want too much arch support as that will fatigue your foot and cause discomfort. You want riding boots that will contour to the shape of your foot. Below I have posted some examples of what I believe are the best riding boots for flat feet:
Roper Women’s Horseshoe Oiled Leather Kiltie Ankle Riding Boots– These boots feature a cushioned insole as well as built in arch support to help support your flat feet.
Ariat Terrain– Features an EVA midsole. Why is EVA a good material to have a midsole made out of? EVA will mold to your foot’s individual shape and contour and then provide solid arch support. EVA is highly recommended for most people with flat feet.
Naturalizer Jersey Regular Shaft– It was extremely difficult to find mid calf boots that are ideal for flat feet. In the end there is not a mid calf boot that I would say is ideal. However, the Naturalizer Jersey Regular Shaft is the best of the bunch featuring an N5 comfort footbed to support your arch and provide cushioning.