two things for this...
1) you can get SR weapons from the disaster fights (even the weakest one) or Catasrrophe fight (you'll eventually want a relic weapon anyway so some SR may drop). If fire is the event's elemental focus, you can get an assault SR from it too. (maybe even one from a raid event if the free SR kami happens to be that element). For this reason, limit break your sword as the event can possibly return and you can get SR to fill the holes until you find something better
2) Never use an elixir to clear any fights outside of ragnarok difficulty (only if you're close to winning ragnarok fights). even then, try to avoid using elixirs AT ALL (you want to be strong enough to not rely on those). This is a waste of them and is even stronger reinforced if you're a free player. The less you spend on this game, the harder it is to get full elixirs and energy leaves... you'll be stuck with the weaker counterparts mostly farmed from the gem gacha