Surely the first thing to do is phone the DWP in UK to find out exactly what you will be entitled to. Asking here will provide you with lots of opinions and experiences, but you want accurate facts.
I would say that many people are surprised by how cold it is in Winter, not helped by the fact that most houses in Spain are not insulated. The cost of heating is high.
Do you require walking aids, or special equipment etc?-these are not provided in Spain.
Spain is getting better with disabled access etc, but many places are not equipped for it.
I am not trying to put you off, but trying to be realistic-have you googled about disability in Spain. You must do lots of research.