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

It depends on how devoutly you believe in your protestant dogma. If you simply believe in the Christian God, and are ok with Catholic idiosyncrasies, then I see no reason you won't want to switch. They are the same basic religion, after all. There are a few differences, but not really all that different than the Protestant Episcopal denomination. If, however, you are definitely opposed to Catholic custom (some of which are vastly different from most Protestant denominations), you should probably think twice before giving up your dearly held position. It is a deeply personal choice, and the only one who can know what is right for you, is you.