If は入りますよ。
次のように書きます：
「If I was born into a good family」
例文としては：「If I was born into a good family, with many good friends, I wonder how happy my life would have been」
映画に出てきそうな文言なので、使うなら上記をそのままご使用ください。
If I had lots of friends who were like-minded and I grew up in a happy home, I wonder how good my life would have been.
この場合、次のような言い方ができますよ。
ーIf I had lots of friends who were like-minded and I grew up in a happy home, I wonder how good my life would have been.
「気の合う友達がたくさんいて、幸せな家庭で育ったなら、どんな良い人生を送っていただろう」
If I had ..., I wonder how good my life would have been. を使って「もし私は…だったなら、どんな良い人生を送っていただろう」と言えます。
ご参考まで！
イギリス 
カナダ 
