Yes you are right that the probability of being pregnant thru oral sex is very very low and unlikely BUT to prevent sexual disease transmission, condom is still necessary.
Love yourself, love your another half. You should consider to use condom. Could money buy health, then spending on prevention is insignificant when comparing to spending on expensive and long suffering medical treatments and drugs. Remember some of the sexual transmitted disease are chronicle, some come back periodically and some are never healed.