Ok, sorry to read about your DC's heart problem, particularly knowing all the problems you have had in the past.
Here are just some initial and probably fairly randomly listed thoughts but do come back to me here or by PM if there's anything else I can answer about our baby or point you in any directions.
Firstly, termination is legal in the UK until term in cases of severe disability, so you have beyond the 24 weeks mark to make that decision, so it doesn't need to be a decision made in a hurry.
Also, a number of people have spoken lots about ARC. I didn't use them myself but other people have spoken of them highly in terms of having an independent person to speak to about results.
DD1 died in utero due to holes in her heart (atrioventricular septal defect) causing hydrops, likely caused by her Turner's syndrome. (99% of babies with Turner's will die in utero, mainly in the first trimester. The ones that survive actually do really well.)
This was all diagnosed after the 12 week scan. At that point, we were offered a termination. That was never going to be an option for us and we declined it straightaway, and, to their credit, even when her death was pretty clear, they never mentioned it again.
We were also offered amniocentesis. I didn't want the risk of miscarriage (around 0.5-1%) and declined this as well. However, an Obs and Gynae friend suggested that should DD1 live to closer to term, we could consider a late amnio where the risk is far, far less and would have a risk of preterm labour. This would allow a genetics diagnosis and might have helped with birth and immediate care planning. E.g. palliative care or delivery near a centre that did neonatal heart surgery. That's something we would have considered but, of course, didn't get to that stage.
Fetal Medicine were fantastic. The consultants were great and the midwives were so helpful and happy to be called to discuss things. Do ask anything, no matter how silly or obvious you think it is, and feel free to ask things again and again so that you understand them. It is very, very easy to forget things you were told in a consultation. Ask them to send you copies of the letters to the GP so you can remember. (In a bittersweet sort of way, I also really appreciate still reading through all the scan reports and notes.)
The consultant might tell you the sex even if it isn't normal protocol. Ours also let us record the sound of DD's heartbeat. I don't listen to it very often at all, but I am glad we have it.
Will have a think in case there is anything else... Will keep you all in my prayers meantime.