Go for a neutral coloured boot if you're looking for it to go with most of your outfits.
Did you read Ben's latest article on two key styles of boot for this season?
I'm a huge fan of both, especially the brogue boot. It's all on personal taste, and I used to be a huge fan of military boots... until most boy bands stylists became a huge fan also. But like I said with everything in fashion, it's all personal taste and the two boots you've chosen are decent!
As for sizing, i've never had a problem. I normally buy in-store, or if I buy online the return policies are so tight nowadays you can experiment with sizes. Maybe go for half a size up, and get yourself some chunky knit socks also!
Hope this helps!