I am saying this with kindness OP. You have been through so much as a parent and you will continue to do so. So I can understand why you would entertain this idea, but I think if I were in your shoes it would not be a good move have another baby. I think it’s OK to feel that you are a complete family with your existing child. Have you had any professional emotional support to deal with your feelings about where you are now, never mind putting an extra child into the family? Noting how the culture around us can really affect how we feel.
I know parents with a disabled child who have said that’ they are longing to have the happy and relatively much more carefree experience of bringing up a non disabled child.
I can totally understand that feeling of not wanting the stress of there being a problem with your baby and alll the worry, financial stress, huge additional time needs, huge additional care needs, which are likely to affect your ability to earn a living as the child gets older. These needs often negatively affect the adult relationships around the parent too, partner of family or friends, Imany of these can buckle under the relentless pressure. Plus the endless hospital appointments, watching your child go through pain and distress as a long term situation, the impact of not knowing the diagnosis, the impact of getting a diagnosis (if you ever do), the strain of NHS care being underfunded and the whole system working ever more slowly. In an ageing society this seems unlikely to be resolved.
You say care needs are sorted but with constant cuts to public services in the pipeline if not already here, you can’t really know this confidently enough, can you? Unless you are a multi millionaire who can afford to outsource everything in the care of your elder child for their lifetime. The relationship dynamic between the kids is a huge issue here, and that applies regardless of finances. My worry would be that, the first child resents the attention the baby needs and hates the noise. The second child then feels angry at and frightened of the first child for the same reasons. Maybe they’d work it out as adults but maybe they’d never do that. You could all be lucky, but the risks just seem enormous.