The problem is I get the impression that OP is looking to have a baby to fill a "void" in her life. She wants a baby to make herself "whole".
Another person can't do that. That's not healthy even in a marriage, let alone in a parent/child relationship.
This is subjective. From my own experience, I found having a child did feel a void. And, no, I don't consider this unhealthy. My DD is not my whole life but she is the centre of it. As a child should be.
To add to these very important points, I'd say there is a big difference between filling a void in someone's life and filling an emotional void within a person. Becoming a parent can undoubtedly give someone a focus and purpose for living and that is a positive thing.
The problem arises when instead of the parent putting the child at the centre of their lives, the child is expected to put the parent at the centre of theirs and is not allowed to be a separate entity to the parent. They are completely emotionally enmeshed.
From the first post and title, it does appear that the OP is expecting the child to give them the love they don't currently have. There's an expectation placed on a tiny human that's not even here yet...it's whole purpose in life seems to be "I've been created to love my mummy". That's not a good reason to have a child.
In subsequent posts, it comes across differently and that the OP's reasons for wanting a child are not quite as selfish as they initially seemed. But only she knows the truth and needs to be honest with herself and, I think, seek counselling prior to going down the donor route.
I don't think it's selfish to become a single parent by choice. I do think its selfish to create a child primarily because you are lonely and unhappy and have no one else. And please believe me when I say, I completely understand where the OP is coming from and have the utmost sympathy for her.