I wanna say the lamp you have there is a full spectrum high intensity light already, so that should be sufficient enough for ground covers.
Now I used to LOVE Lilaeopsis Mauritiana in my previous tanks, which is a micro sword with real narrow leaves and forms a nice cover by its runners (sorta looks like grass really) , provided it has everything necessary for good growth (proper nutritious water & proper lights).
However since I couldn't find that when planting my new tank I bought dwarf baby tears, I can not yet tell you about its growth rate since I just planted it few days ago but as for the looks, I love it and it stay's real nice and low (~0.5" or less). However those apparently are recommended for pH 7.5 and LOWER when I was reading up before buying them, so you may want to consider your water parameters there.
A nice and definitely fast growing alternative is some Java moss tied down to a mesh of whatever size you want to cover and have it cover the ground for you. However the 'downside' of it is any rocks or DW will have the Java growing on it too UNLESS you regularly maintain it.
Hope these options help you.