I completely understand your desire to have another child. I only have two DC - twins - and it took a lot to come to terms with the fact that I wasn't going to have another. I did consider it up until the age of 42-ish but it wouldn't have been the right decision, no matter how hard that was for me to accept.
It's very easy to encourage you to go for it. You're not really that old in the grand scheme of biology.
However, a PP - apologies, I've forgotten your name! - mentioned the worse case scenario thought process and that's a really good approach.
With that in mind, what if your baby is autistic? And has high needs like your eldest DD - could you cope with three young children, all close in age, an older, autistic DD with high care needs - plus a F/T job AND you're planning to build your own house.....which will be stressful as hell no matter how organised you are.
Could you cope with all of that? Could your relationship cope with all of that? Would you be depriving your existing DC of the time that you give them now? Bear in mind that a 1yr old doesn't need anywhere near the level of input that a toddler, pre-schooler etc does?
And I'm sorry for sounding negative. I don't mean to be. I read your post and my heart immediately squealed yes! Another baby! I'm just trying to think through the toughest scenarios so you can ask yourself the hard questions.
For reference, both my DC are autistic, and DS has high needs too - he'll be at home for life. I'm also autistic/ADHD myself. My questions about considering neurodiversity aren't intended to be derogatory but just a question about whether you have the capacity to support more than one neurodiverse child (as there's a higher risk with a) an older birth mother and b) where there are other autistic family members). Just something else to throw into the mix to consider.
My DC absolutely rock. They are both wonderful people and I wouldn't change a thing about them. But my son's needs are the reason we didn't go ahead and have another baby. I realised that I couldn't give a baby and DS the full attention they both deserved, let alone DD too. And DP and I had the conversation too about another child being autistic - not that there's anything wrong with being autistic, but as we know, it often means greater care needs/greater support. It nearly broke my heart to make the decision but a few years on I feel totally OK with it now, and I know I did the right thing.
You never know, maybe the universe will take it out of your hands and you'll have a genuine accident and fall pregnant! :)