It is gonna be a bit harder with you being a smoker

[ROBINDESBOIS]

is this sentence OK?
It is going to be harder with you being a smoker.

[Rusty]

Yes.

It's going to be harder, with you being a smoker.

If quoting colloquial speech:
It's gonna be ...

[poli]

The "a bit" that you used is OK. It just sounds a bit British (and east coast USA I suppose).

[Rusty]

I've heard 'a bit' used everywhere I've been in the USA.
It's a good qualifier for 'hard', but means that it won't be a walk in the park. We also use 'a little,' 'a tad,' and 'a wee' (but the latter two seem less used (one more British and the other more Scottish)).