It would be helpful to take a pic of the underside of the cap to see if it had gills or something else. My suggestion is not much better than yours ...
I had tried to take a photo of the underside of the cap, but the mushroom was quite small and I could not get my smartphone camera low enough to look upward at the gills. I did not want to uproot the fungus to take a better picture. Now back at home and looking at my fungi field guide, I wonder whether this may be an young Bolbitius titubans, with a "yellow to greenish cap, egg shaped when young....found in grass in disturbed areas". The mushroom was in the Mount Majura horse paddocks, which matches the "grass in disturbed areas" well.