The KZs (ZS10 Pro) are very good and they don't cost a lot (50$).
I have the same IEMs.
I've only used them once or twice - nice, but I still prefer an amp and a wedge for vocals only. I like to hear the band in the space.
This is a rhetoricl question - but what's the difference between using a "monitor" and an "amp" to monitor yourself?
One is in front of you, and one is behind you?
If the option really is no amp, but a floor wedges is fine - I'd buy a QSC CP12, and use my pedal preamp of choice plugged directly into Ch.1 of the QSC. Then, basically you have an amp - but it looks like a floor monitor.
I'd split the signal - one to my monitor / secret amp, and then a dry signal (JDI or something) to the house.. You would have total control of your "amp" and the guys would be none-the-wiser. They could mix in what ever signal you are sending to the house in their wedges or IEMs.
If you need vocals, then run your aux mix into channel 2 of your wedge and mix in what ever you need (vox / guitars - but not your Bass because you already have that in there and have separate control over it).
HPF / LPF or cab sim probably needed (Q\strip or something). At that point, you basically have an amp, but the other guys in your band will think you are using a monitor - because it looks like a monitor.
All this to say - it's probably an aesthetic type thing, so make a rig that works for you and them.