Sizing issue

I wear Edea Overtures size 250C. Currently my heels slip off the 'cup' which I find really frustrating.

I'm planning on getting the Risport RF3 Pros. My feet measure 230mm. (Before anyone says this: no, I dont have any skating shop where I live and I cannot travel to any skating shop other than to some other country.) I contacted a virtual fitter to whom I sent pictures of my feet and measurements and they said 235C would be perfect for me. But it wasn't in stock so they said the 240C would also be ok. I just don't want my feet to slide in my boot like in my overtures. Should I choose 235C OR 240C. Does anyone here have those sizes? What length measurement did you get for your feet?

Also, I found this sale for 235C boots and blades too at a super low price (I'm on a low budget) so would the 235C be ok?