There will always be people to try and talk you out of it, and raise all the sprectres of infertility and pregnancy loss and disabilities. Seeing as how you are already at the point of considering another pregnancy, and don't see to be a moron, I would assume that you are already well familiar with the risks of pregnancy in one's forties. You've not asked about those, you've asked if it would be selfish of you. Most women get pregnant for selfish reasons. None of us know how it will turn out. I hope that if it is what you want, and if you think it will be best for your family, you will do it and not be afraid. I understand that it is a big decision, but I really don't think that you are going to get much useful advice or perspective (including my own) off an online message board.
I am stepmum now to two teenagers, because their own mum died of cancer in her forties. I have a baby girl, too. Her dad will be an 'older dad'. All of our lives are immeasurably happier because she is here, and we are all devoted to her. Selfish? Maybe, but I challenge any other parents to say that they are doing a better job than my DH and I, because they are younger . The thing is, you know yourself what you can provide for your daughter. Few people can bring a child into the world with absolute certainty that the child will be happy, or financially secure, or destined to have two parents until he/she is grown. Risk is part of life...when we are thinking of having our first child, people say to us "oh, there is no perfect time!"...and I guess I'd say the same is still true for you.
And at 15 or 25 or 35 or 45, as a prospective mother-to-be, there are things you can do to improve your chances at a happy, healthy baby. There are some studies showing that older mums are actually at an advantage in some respects. So if you are serious about wanting to try again, start preparing now... Get your health into the best shape it has ever, ever been. Change your diet, get more exercise, whatever it is you could do that maybe you haven't before. Go over your finances - set up savings plans and insurance policies or increase the ones you have. Make sure you are happy with your Ob-gyn, or look for one who you like better. Take all the negatives, and address them as best you can. and then let go. Good luck, whatever you decide.