We bought a belt from Doc that was about 4" x 24" and filled with old lead bars. (The lead was thoroughly discussed in a previous thread.)
We liked it so much my wife sewed another one that is 8" x 24". They work great and are not uncomfortable. We drape ours over our thighs, not our waists.
We float whether we have suits on or not... but I noticed that baked beans, cabbage and boiled eggs tend to increase the "float" as well as the bubble action.