Una, I always go for a 6 in boots, that way you can wear socks in winter. I am a 5 1/5 in sandals and heels usually.
Good luck with the boot search. It was a long one for me. When I found a pair of boots that were perfect for me, I just tried to duplicate the measurements in circumference and shaft height. I searched all over, by the end not really even looking at cost because I was so frustrated. I ended up finding the perfect pair on ebay. It was risky but I had my measurements in hand and I finally pulled the trigger. They ended up being the perfect black boots. I hope the ones from DSW work out for you. I like some of the stuff on their website but the store always seems like last season's rummage sale to me. I hardly ever find anything there