I walk all day for work (I read utility meters) and at one point was walking anywhere between 5 and 20 miles a day, 5 or 6 days a week. I've been doing it or more than 5 years now, so you do learn some tricks of the trade.
I normally wear a women's size 8 or 8.5 US, depending on the shoe. For my work boots (standard issue hiking boots from Big 5 - I catch them on sale for half price at $40) I buy a men's size 7.5 US, which translates to a women's 9.5 or 10 plus some additonal width. I honestly go that much bigger, and I've been doing it for years. I use standard athletic socks with the no-seam toe and it works great.
Being that they're high tops, you canget away with a little bigger without the heel sliding all over the place. The only problems I've had were when I tied them too tight, but that's a no brainer.
For men's shoes, see if you can go up a half size or even a full size, and/or maybe try a wider shoe. Your toes really do need to be able to wiggle around a bit. Just don't get them if they slip around on your heel. That's the fastest way to a nasty blister.