Bestow Curse says
At the DM’s option, you may choose an alternative curse effect, but it should be no more powerful than those described above. The DM has final say on such a curse’s effect.
Would "While Cursed, The target has vulnerability to a damage type of your choice" be a balanced alternative curse effect? This seems like a fair trade to me because the target gets to act normally every turn and you essentially halve its hit points, as compared to the 3rd option:
- While cursed, the target must make a Wisdom saving throw at the start of each of its turns. If it fails, it wastes its action that turn doing nothing.