Wearing "conductive shoes" instead of heel grounders?
I have not seen these before, and I can see issues for certain work environments in that there isn't really any foot protection against falling objects and crushing so OSHA (in the US) might have an issue in some environments.

What I can speak to is that often gowning rooms also provide socks as well as the ESD smocks and particles containment bunny suits.  So it's possible that you could use your standard socks (especially if you've passed ESD testing at the metering stations) with your present socks and heel grounder solution.  But you have the fall back on ESD socks.

If you are in a ESD controlled environment, then presumably you have a regular schedule of testing that you have to go through.  Your ESD people should be able to quickly evaluate that.