this has had me so upset for you.
you shouldnt blame yourself for this at all, i have 2 friends who have been through very similar losses, 1 went on to have a healthy daughter getting pregnant straight away after losing her little boy, and i know she felt exactly the same as you, she longed for that baby so much but she was never meant to be a replacement. (she also had another daughter a couple of years later)
my other friend has chosen to be sterliised, she already had 2 sons, lost her 3rd at 36 weeks (cord came first) and she couldnt bare the thought of it happening again. its been a year since her loss and she is still dealing with the very raw pain of it.
i suppose what i am trying to say is, YOU know whats the right thing for you. i hope so very much you hold another baby soon.
sending a prayer for your angel Ollie xxxxxx