Vulcans do use contractions
Neither Memory Alpha (and here) nor Memory Beta make any reference to this 'rule' of not using contractions.
In fact, we know it's probably false:
In TOS 'The Paradise Syndrome', Spock says the following:
SPOCK: There isn't time, Doctor. I must decipher those obelisk's symbols. They're a highly advanced form of cipher writing.
In ENT 'Awakening', we have a couple of instances:
SOVAL; I could protest, but it wouldn't accomplish anything. V'Las isn't one to change his mind.
T'LES: Syrrannites believe that Vulcans have strayed from the teachings of Surak. Considering what the High Command has done in recent years, the listening station at P'Jem, the suppression of dissent, our position isn't so hard to accept.
In ENT 'Doctor's Orders', T'Pol says:
T'POL: I'd like to complete the diagnostic.
We have concrete evidence that Vulcans do use contractions. It is fair to say that Vulcans don't often use contractions, but they occasionally do.
So, relax; you don't have to give up contractions!