Choosing words to sound "professional" is affected speech. Most people who do this end up sounding like a poseur.
There is no reason to use a fifty cent word when a penny word will do. Word choice should always be guided by which best expresses your thoughts; not to sound a certain way.
Many professions do have their own lexicon but this is largely because their terms have more precise meanings than the words used by the general public.
Of course, certainly, absolutely, affirmative, beyond a doubt, exactly, defiantly, undoubtedly, precisely, unquestionably, indeed, indubitably...
of course. absoutely. certainly. sure thing. positively. and i'm sure there are plenty more :)
There is no doubt in my mind that you are right or its true ( its way too long to say XD)
Indeed, Of course, Absolutely, Precisely, Agreed, Certainly, That's right
Well there's other phrases. I agree, I concur, things like that.
Exactly. Absolutely. Yes Mam/Sir.
Definitely can also be used.
AFFIRMATIVE :P Do it