I am very similar to you, but 35. For a long time I've known I didn't want kids but have only really become comfortable in the choice the last couple years because I think there is so much spoken and unspoken expectation on having kids, and not doing so must be due to some sort of failing (physical, not finding a suitable partner in time, etc).
What's made me more comfortable is growing more into myself and becoming increasingly confident that the life I want isn't compatible with how children will change it (at all stages). I appreciate there are so many wonderful things about kids / a family but I just simply value my independence and flexibility in life more.
I've gotten more friends in my circle recently who are older (40s, 50s) who have chosen not to have kids and this too has given me confidence that a child-free future can indeed be as great as I imagine it. Will I regret it when I'm 90 on my deathbed? I don't think sacrificing many decades of the life I want for a hand hold right at the end is worth it. Across life my my focus is on building a community around me for mutual support at various life stages and circumstances.
I have a DH - We've been together 15 years now, married last year. He feels exactly the same. We are very financially stable (earn £250k+ between us) and have supportive families who would happily help with childcare etc, so it's not because logistically or financially we would face undue pressure. There are just so many other areas of life we are fulfilled by and don't want to compromise on in the short or long term. We have a niece, god children, and friend's kids whose lives we are really active in, but it's just not what we want for us.
I think discussions and experience sharing on this topic are so important so that more and more women can decide if children is/isn't for them rather than just going with life's unspoken expectation.