May be you could try oxygen plasma treatment to make the surface more hydrophilic. 

http://dx.doi.org/10.1080/10408436.2014.1002604

graphene oxide is hydrophilic itself. If it is not, maybe the procedure got wrong. Try this method: https://www.researchgate.net/publication/287798548_A_rapid_and_eco-friendly_route_to_synthesize_graphene-doped_silica_nanohybrids

I was able to prepare a GO with a C/O content equal to 1.1. It was my best result in terms of oxidation level. Good luck!

Article A rapid and eco-friendly route to synthesize graphene-doped ...

It depends on whether you want to do it top-down or bottoms-up. From a bottoms-up perspective, the simplest way to make highly hydrophilic GO (C:O < 1.8) would be to leave it in the Hummers/Staudenmiers/Tour's rxn mixture for 48-72 hrs, or even longer. From a top-down perspective (i.e.: if your GO is already pre-prepared), you might actually want to think about doing the same thing, i.e.: blending GO with the oxidants from one of the three methods outlined above, leaving it to oxidize for 2-3 days, then recovering and analyzing the product.  

Article Preparation of lipophilic graphene oxide derivates via a con...

Graphene Oxide is already hydrophilic, it is very easy to dissolve GO into water at RT.