Whether you have children or not life will likely throw some curved balls at you and not turn out how you expect.
My children are the best thing in my life and I have never regretted them for a second. However, life is not at all what I anticipated when I made the decision to have them.
I was on the fence. I wanted to be a mother but after experiencing an appalling childhood I was very worried I would not be good enough or know how to be a good mother, with no model if good parenting to follow. I also have health problems so worried how I'd manage from that perspective. Ex-H persuaded me it would be ok, and that all parenting etc would be 50/50. We had a detailed plan. With those assurances I thought it would be manageable.
Then when they were babies he walked out. Now has no contact at all. He has caused huge damage to them. And I'm now a lone parent trying to manage children with disabilities, my own health and a demanding professional full-time job to provide for them. No family help.
So even if you do everything "right" (well established long-term relationship with someone with a good job and income who seems stable, well-established and paid career yourself, agree in advance to equal parenting, already own a home etc) things can change overnight.
My advice therefore, would be not to have children unless you are confident that you could cope with raising them alone - financially, physically and mentally - if your partner should die or leave. Nobody thinks this could happen to them, but it does. And whatever you do, make sure you continue to ensure that you have and maintain the means to be financially independent and provide for them alone if necessary after you have them, if you do. I am grateful every day that I ensured I had a well paid and flexible career before having them, otherwise their lives now would be very, very different.
But despite all of this, I do not regret it or wish I could change it. I am very sad for them that they do not have a father in their lives and the impact of that on them. I am not sorry for their existence, and the purpose of my existence now is to provide everything I can for them, financially and emotionally. But that is not miserable, it is a huge priviledge, being their parent. It does change you and your priorities entirely but brings meaning and purpose to life and a boundless, unconditional love that could not be experienced any other way, far different to and exceeding what could be possible to feel for a partner or other family member. But without experiencing that you wouldn't miss it because you'd never know it.
There are negatives, of course. The responsibility, especially being the sole provider for all their living costs. The worry for their wellbeing and what kind of lives they might have as adults. The knowledge that any life includes some suffering and that I made the decision for them to bring them into existence and therefore for them to experience that, but hope that they will find love and fulfilment and happiness that outweighs this. The hope that I won't pass on my own traumas. What they will think of me when they grow up and will they think I've done a good enough job, that they had a good childhood? In the end the only judgement of a parent that matters is the child's own judgement as an adult. I've not been able to spend as much time with them as I'd hoped because of our circumstances, which makes me very sad. The drudgery of all the physical and mundane work is huge and exhausting and this makes my health worse, but will improve in time I hope as they get older. Things I wanted to do with them but now can't afford to, on top of being sole provider, make me sad to think of (more holidays for example, to show them the world, while they are little sponges that find everything fascinating. But impossible while paying mortgage plus another £2k childcare per month!).
Having children will mean a lifetime of conflicted feelings and worry in one way or another and usually (based on the mothers I know, whether married or single, SAHM or working) always some guilt. It is a huge and lifelong commitment to put someone else first always however, that part is easy, because you love them so much you want to. Someone said to me once that "parents are only ever as happy as their unhappiest child" so it is taking a huge gamble because you have no control really over how that will turn out, no matter what you do.
Life would have been far simpler without them here I suppose: practically, financially and emotionally. But far less meaningful. The joy I have at their curiousity about the world, their love for each other, watching their personalities emerge and that I will have watching them grow into adults. If I try to imagine what my life would have been without them, I think I'd enjoy the first week or so of rest and then feel empty. But I wouldn't know what this fulfilment and love felt like so I suppose maybe I wouldn't miss it, and would be enjoying lie ins and lovely holidays like I used to have regularly.
It is a double edged sword indeed and like anything worth doing is hard work and involves opening yourself up to the risk of tragedy. I think our pursuit of "happiness" is often misguided. Nobody feels joy all the time. For me life is about purpose and finding your own meaning and contentment. But there are many ways to go about that and people are all different, thank goodness.
We can never really judge the path untravelled because we do not know where it would have led. We are all, really, making decisions in the dark. And:
"Thus we never see the true State of our Condition till it is illustrated to us by its Contraries; nor know how to value what we enjoy, but by the want of it."
Robinson Crusoe, Daniel Defoe.
Good luck OP, whatever you decide.