You are in the same situation I had with my first boat. The main sheet attached so far forward, that there was no downward leverage on the boom. 2 things I did, one was the boom vang, which I occasionally used, but what helps more was moving the attachment point farther back on the boom. I left the main sheet traveler in the same place, but the main sheet actually angled back to a point farther back on the boom. That ended up being very practical, as the leverage down on the boom was dramatically improved. Technically you only need the boom vang when running down wind, although you will find getting the main sheet attachment point back farther does a lot. Having the main sheet angle back did not seem to hurt the functionality at all, and actually improved the downward pull on the boom when running down wind.
Get yourself a new bracket for the bottom of the boom and rivet it on. That should be quick and inexpensive. See how much that does for you. Sure a boom vang can help, but just moving the attachment point on the boom gets you about 70% there because of the main sheet angle.