I just bought New Life Spectrum Small Fish Formula .5mm Sinking Pellets. They are TINY so any fish should be able to eat them and they don't sink that fast, so your hungry betta should swoop in and eat them well before they hit the bottom. First two ingredients are antarctic krill meal and herring meal, then wheat, protein is 48%.
Coincidentally, based on what everyone's been saying here, I decided to cut down on the freeze-dried bloodworms. Before I fed two a day. Today was first day I did this and this morning, when I reached for the pellet container instead of the bloodworm container, my male went into a frenzy. He kept looking at the bloodworm container, then at the pellets and back. He finally ate the pellets then swam over and pressed his nose against the glass staring at the bloodworms. He has a betta log tunnel on that side and he's been spending much of the day inside it, staring longingly at the bloodworms. It's been so funny to watch.