Doc Martens sizing is confusing. :/. There are no half-sizes*, and some people are adamant that you can size down a full size, and some will be equally adamant that you cannot. And of course, feet are three-dimensional, we find different things comfortable, etc.
All that said -- the unisex styles tend to run a bit bigger than the women's styles, and I've heard that the made in UK ones are also a bit smaller. For myself, I am a true size 11 (US women's) and I find that I like size 11/UK9 best for all boots and for women's oxford styles, but can sometimes size down to a 10/UK8 for unisex oxfords and the platform oxford styles. And yes, insoles and heel pads can help with fit when you can't size down. Hope that helps!
*at least in the US -- I think they do carry a few (but not all!) half-sizes in the UK.