It may well be possible to fall pregnant with just one attempt whilst on Clomid. However, due to Clomid potentially changing your cycle it may not be as easy to predict ovulation and therefore plan your one attempt.
The thing with Clomid is that you really want to get pregnant as soon as possible whilst taking it as you only have a limited number of months you will be allowed on Clomid. If you are confident about yours and OH's high fertility, I would try one attempt for the 1st month only. If it works, great. If not, move on to more attempts in the following month(s).