Here's my experience if it's any help. I found myself unexpectedly pregnant at 47 (in Ireland not UK). Already had 2 teens but my DH is 3 years younger than I am.
Went to the GP when I got a positive test and freaked out. He just referred me to a private OB who saw me pretty quickly.
At the OB she had a scanner and dated the pregnancy. I was 13 weeks along already. She said that she couldn't see any obvious signs of trisomies etc and I found that reassuring, although she did warn me occasionally they don't show up with anything visible at that stage, but said usually she would expect something to look very obviously wrong at 13 weeks if there was eg trisomy 18/13/21 present.
Then I had many weepy conversations with DH, but the most helpful person was actually a friend who had also had an unplanned pregnancy in her 40s. Many chats and sleepless nights later we decided to continue. Did the NIPT and had no issues there. Felt reassured by the 20 week scan being ok too.
The pregnancy in the end was totally fine - I stayed very active and had an easy enough birth - one stitch. My previous pregnancies/deliveries were similar. Baby is now 2 months old & I'm BFing him now. Nothing obviously wrong with him and he fits right into the family, it's like we always planned this.
But also we are in a pretty good situation in that we have paid our mortgage off, have quite a big house, have flexible jobs etc so "can we afford this" wasn't as much of a consideration for us. Also we're both otherwise healthy, and the older kids don't have any special needs or anything and have been very into the whole thing. They adore the baby now. Again this won't be the same for everyone in this situation.
Like you I wanted to be fact based in my decision making and I had no illusions about my age at all, I knew things were far higher risk. But those risks did not come to pass in our case. And the facts you need I think are actually not about risk levels etc but about what applies to this specific pregnancy - so you need to have a scan, have an NIPT etc and THOSE will give you the facts you need to make your decision.
Hope this helps, it's a terribly anxious time, best of luck whatever you decide.