Frosmoth is not a bad option actually, if you take a second look kyurem doesn't need to discard water energies from itself, you can attach the energies from your benched Pokémon and discard them for the attack just like blacephalon GX or dragon Majesty's turtonator
Sure thing but Kyurem does not last more than one turn and you will need to stream them. This would force you to run Froslass in addition to Frosmoth to power up the next Kyurem once the currently active one is defeated. It is not an issue about getting the energy into play to discard them. the issue is to stream Kyurem without making the deck clunky.