Hi mate, I'm a first-year at Hatfield and absolutely love it. It is an amazing college and extremely well-rounded in terms of academics, sports, and music etc, and is super close to town and pretty close to the science site (where most of the first year lectures are). You are only likely to get an ensuite if you have some sort of disability, otherwise, it is highly unlikely. Honestly, I think it is unlikely there are 90 single ensuite rooms at Hatfield, although most (not all) share rooms have an ensuite. I understand you don't want a shared room, but then you might have to forgo the ensuite. However, there are a couple of single rooms around college which are ideal (without ensuites), meaning that you might have to share with only 2/3 other people. I would defo recommend choosing a bailey college just because of convenience, and from my experience sharing a bathroom is honestly not bad at all and in many cases over-exaggerated. When you fill out the college preference form in August/September make sure to state you defo want a single room, and then you are likely to get one. There are also a couple of shared rooms which are kind of singles, as there is a wall and a door separating them, but the 2 people in that room share the same bathroom.
I will also add that if you want Hatfield make sure to have it as your first choice as it is generally over-subscribed (alongside other bailey colleges + St.Marys.).
Hope this helps, and let me know if you have other questions!