Do you think it would be okay for me to switch from Christianity to Catholicism for my girlfriend or wife?

You would not be betraying God, or Jesus, or the holy spirit, if that's what worries you. In fact, I think it is valuable for people to learn about other religions. That doesn't mean you have to sign up. Since you already did, explore away. If you decide to leave in the future, and then want to go back, they have a Mass where all your sins, even severe ones, can be forgiven, around Easter time.