You can use anything to produce and mix, provided you know how music should sound on it/them. Just be very careful, you'll miss things such as phase issues and you may under-compensate for bass with headphones.
But it's all about habit. Any sound device of a certain quality can be used to produce stunning results, if you know every nuance, every weakness of what you're listening to.
With mixing on headphones, it's always handy to have some speakers to double check on. Even if they are only laptop speakers (though something bigger would be better)
Also, I've read a lot that eletrostatics need a bit of power to drive them properly. So a decent amp would help.
I have some monitors, and some Bose speakers that i test back and fourth. Until i get some new monitors i guess ill be using these.
I check with mutiple speakers, headphones, and my car system.. I just need more experience with EQing/mixing in general, nothing is loud enough and i don't want to over compress anything or just through a limiter on the master and crack it up.