Being an only child is not a bad situation, so I don't know why you're contemplating bringing a child into the world who will almost definitely not have a father just so your first child will have a sibling. I'm not being judgmental, nor am I meaning to be harsh, even if it comes across like it.
You say, "I don't see that I have many options at this point" -- if artificial insemination didn't exist, then you wouldn't be feeling this pressure. At least, I assume you wouldn't go have a one-night stand to get pregnant naturally, knowing that neither the father nor any other man would be in the child's life.
It may be that not too many months in the future there will be a nice man with several kids who will meet and marry you, and your daughter will have siblings like you want her to have... except that if you're pregnant he will assume you're taken so you'll never even approach you. Maybe.
Adoption is always an option -- to take a child who has no parents and to give him or her one parent.
Finally, in the "man" department -- I'd suggest the blog "What Women Never Hear" at http://wwnh.wordpress.com for suggestions on how to meet a guy with potential and make him a keeper... or find out that he's not worth your time so you can send him on his way before he takes up too much of your time.