Peter why don't give Age Northern Ireland a ring and they will help you out...it is a freephone number. They may be able to give you some extra help and info too....
Age NI Advice Service
For advice & information call freephone 0808 808 7575
I'm from NI. We used respite for mum when she was in the mid stages of the disease. She's now in a nursing home full-time.
It was organised by social services but I think you can approach homes directly if self funding. Ring any one of them and they will be able to tell you about their admissions procedures. GP should also be able to advise.
Think respite is around £500/week or more depending on the home if fully self-funding.
Do you know whether that would be the case? You can get an assessment done if you are not sure. Social worker or GP could arrange this.
Where are you exactly? I could name some places that I have experience of in private message as we are not allowed to mention names here on the public forum.