Re eggshell... We have water-based eggshell in the kitchen and it's not as durable by the way.
Also, I'm not sure you can over-paint an oil based paint with a water based one if you want it to stick. You may need to remove the gloss first, rough it up significantly, or maybe use a coat of something specialised in between? You maybe should check this out.
If you are painting over gloss why not look at an oil based eggshell? We have this in our hallway and it's been pretty durable without the stark shine of a gloss.