Jeanie, I think the heel always slips in flat boots. I did a compulsive research on that a few years ago and found that they all slip, at least on me, and my heels are not narrow. I hope your boots widened overnight...
Joy and JayS, I listened to what Suz suggested and tried them first thing in the morning. I realized that the ones in my size rub a bit on the little toe so it looks like my size is ruling itself out and I will need the half size larger. I did try them with trouser socks and not stockings. I may want to wear them with tights but on very cold days I will need my thicker socks.
JayS, I am glad your boots are working out for you. Enjoy them!
Suz, maybe if you will wear your boots with a dark coat or jacket they will work for you? I can't wait to read your post on these boots.