One could say how interesting it is to read everyone here so concerned to find the solution that works for "mommy"..... You forget the most important thing in this whole story, IT SHOULD BE IN THE BEST INTEREST OF THE CHILD.
I understand that this is something you may not be aware of, because we have all been spoon fed the happy utopia crap by adoption agencies, sperm banks, surrogate agencies and everyone else who stands to profit money.
But here is the reality...I have read dozens of impartial studies and HUNDREDS of testimonials from "children" (DC- donor conceived, surrogacy babies, adoptees), who are now adults and are speaking up against and for the reform of the current system.
Your egg or not, that child would have grow and bonded with another woman, in her body, and for all intense and purposes, as far as that baby is concerned, she is his mother. No matter how soon you do it, that child will suffer from separation anxiety. And one of the worst things you could do, as you have already suggested, is to not tell the child at all.
It is a very complicated situation and one most people take too lightly. I urge you that you start reading blogs from adults born of surrogacy, surrogate mothers and "parents"...and not the "all is peachy" ones, but from those who have been through it and are now arguing against it.
I am not saying it cant work, but your first concern should be how it will affect the child. And this is something that will affect him/her, just because we choose to ignore or guilt them into hiding their loss (and it is a loss), it wont mean that it isn't there and that one day you wont end up with a child who will be labeled "angry" or "you just had a bad experience" (it is not an easy thing to digest that most of these "children" had happy childhoods, are successful adults, and yet they are speaking against it all).
Wanting to have a baby (regardless in what way), and regardless of how selfless we plan to be as parents, is primarily a very selfish want. If this is the choice you make, you owe it to your child to educate yourself on all the additional problems and feelings they will face. Please remember that things should ALWAYS be done in the best interest of the child.