If there are long intervals (>1second) where you are not speaking you could use a noise-gate to squelch the (very faint) hiss to true, flatline silence during those intervals.
You can get a free noise-gate for Audacity here … http://wiki.audacityteam.org/wiki/Nyquist_Effect_Plug-ins#Noise_Gate
Also try the use the DeClicker plugin (here) on default settings. It’s not a noise reduction : it’s click reduction , which makes the VO sound more polished.
Maybe this is just my hearing , but I’d Boost the treble : IMO the “th” of breath isn’t loud enough , boosting treble will make it louder.