Buy around 12 of fire resistan potions and 8 of the rest, max out to 8 every atribute and after the third battle stack up again to 8 all
You can buy an alchemy work station from Tale. Go to each location you have unlocked and collect the herbs there by click the little plant icon in bottom left corner. Go home to the set up workstation and make them yourself if you found empty vials via the stray dog or you bought them from Lazarus. Or yeah, just buy the potions for 8 gold each from Lazarus.