Try several pairs on. You will probably find different sizes are needed in different brands. With varies too. Dont buy too short but a wee bit narrow initially is OK. Try them on with the weight socks you will be wearing and after exercise when your feet are swelled.
Order several pairs from places with a good return policy or visit a place like REI etc where you can try multiple brands.
Unless you are 22 years old or less, substandard footwear in tough country is not a good idea, not good at all.
