I would go with option 1 renting, at least for a while, to see if you actually do want to live together.. if you get a rental agreement with a 6 month break clause, if the worst comes to the worst, you are only tied to living there for 6 months. (i.e. you can give notice after 4 months, with 2 months notice).
If you go down option 2 route, you are commited to a mortgage of it doesnt work.
Also, with both options 2 and 3, if she is living in the property with you, that you own, especially with kid, she could in theory have a claim of having the right to live there, which would make it hard to get her out if you split up, even if she cant claim part ownership (hard for her to do without marriage).
Whereas if you split up and are renting, she can only live there as long as the rental contract lasts.
So, number 1 Is the way forward... at least until you are a bit more sure of each other.