I had the exact same problem during my OW, and also had problems descending (needed 24 lbs to get down; now I use 16). I thought about ankle weights, but my instructor advised me not to get them. I found that in my excitement and all, I really was subconsciously finning a bit. The staying at the surface was aided by shallow breathing. I was fine while finning, but during the stops, I would end up with my feet up in the air, despite having Volos, which are slightly negative.
By relaxing more in the water, despite wearing 6.5 mm boots, I don't have the foot float problem anymore, and I'm glad I didn't go with the ankle weights.