I was never that bothered about having children either, but I'm pleased now that it happened. (Fortunately.) I also relished my lie-ins and lazy time and I'm in the middle of a mist at the moment with tinies, but I'm sure those days will return (to a certain extent).
What I will say is that my concerns regarding the latter have been alleviated somewhat. You will cope with less downtime because you have to; and your own children (though looking after them is tireless, thankless and often mundane) are not as boring as other people's. Or rather, your looking after them has to, and can, be reconciled with your own failings and requirements – so when looking after my gorgeous nephews and nieces, I would never bark at them to entertain themselves while I have to do the washing up, or declare I want to sit down for five minutes with a cup of tea and leave them to their own devices – as I (have to) do with my own – so looking after them is more exhausting in the short term.
And you'll find your own rhythm, with time – perhaps you'll enjoy watching some TV programmes or films together as a weekly ritual, or they'll learn that Sunday mornings are the time when you lie in. You have to sacrifice those things for a while, but I do think teaching your children to have patience and respect for your own modest desires and foibles is important, not simply selfish.
Finally, having children has made me mature in a way I might not have, as I was never especially domesticated before. I am much more efficient now than I was, tearing through chores and jobs and able to survive with less sleep, so it might not be as hard as you think, in those ways. On the other hand, having them has opened up a whole new emotional terrain; I am so much more anxious than I was before. Before, I might have worried about walking down a dark street at night, i.e. I was naturally concerned about my own safety, though not overly so. Now, every day, and even more so when they're ill or sleeping badly or tantrumming and I don't know why, I am filled with terror and dread that something awful is going to happen, to them; I sit there feeling like it's Sunday night, with an exam the next day. I don't know if this is a normal experience, but it is horrifying and I don't know how to control it; everyone else seems to be in control, but maybe everyone feels the same.
So, basically, I'm sure you'd be a fit mother. It's easier and harder that I, for one, expected, in so many ways, but also very rewarding, yes. I wouldn't change it, myself, but I have no doubt your life could be fulfilled and exciting without them.