Size 9.5 Extra wide fit women's slippers in the UK
British high street chain Next has over 400 of their own shoes & boots range in size 9 uk (43 eu) online, although they may be rare in store. They also have footwear in sizes 10-12 UK from other brands including Yours, LTS & various sports brands. Their website navigation is not great on desktop, so I've linked directly to the Next brand size 9s as a starting point. But if you click on view more/all under the size filter list on the left, you can choose other sizes.
Specialists in extra wide shoes, from 2E to 8E widths. Mainly comfort and traditional styles with over 100 size 9 uk options. Smaller range of size 9.5 & 10 uk styles, with a few trainers etc going up to size 12 uk / 46 eu. You can also order a catalogue or view it online to see the complete range. Their width finder tools only go up to women's size 8 uk unfortunately.