Something with range would make sense or something that can take physical damage for you or that increases unpredictability of timing or direction of attacks so they have more to defend against. A weapon like a tail or a armour would make sense. The shield takes damage in place of your body for some hits, allowing you to last longer. A ki-infused boomerang could help. It would be like Freeza's discs or Piccolo vs 17.
Sharpness of a weapon alone might do nothing since Trunks blocked Cold's sword attack? But Piccolo's makankosappo is extra potent due to being piercing attack, same for Krillin/Freeza's kienzans, so sharpness should matter. Maybe Trunks didn't infuse the sword with ki and it was just his swing power doing the damage. Maybe they can't put ki into a non-living object without wastage. They can put it into thejr clothes in a thin aura layer around them, but a sword is further away they'd have to make a wider aura and waste a bunch of ki, if they can't control tje direction of it.
