I was thinking about what Bayern Munich needed to improve to be stronger next season... I assume it is obviously the defending. They conceded 45 goals in the Bundesliga last season which is huge for a title challenger. 
They don't need any transfer for the attacking line. They were the most productive team of the season by 94 goals you know. The only thing they can do is to find someone for Choupo-Moting's place as he is leaving. They were looking for a centre-back as far as I know. Jonathan Tah is a target for them currently. He would be a great addition honestly. I don't think Upamecano is performing well. He tends to make simple mistakes a lot. Tah might be a good replacement for him.
They don't need any transfer for the attacking line. They were the most productive team of the season by 94 goals you know. The only thing they can do is to find someone for Choupo-Moting's place as he is leaving. They were looking for a centre-back as far as I know. Jonathan Tah is a target for them currently. He would be a great addition honestly. I don't think Upamecano is performing well. He tends to make simple mistakes a lot. Tah might be a good replacement for him.
But one more thing that is the main factor is the right manager to handle Bayern Munich because after all, if Bayern Munich makes a mistake or is wrong in choosing a manager then it will be difficult for Bayern Munich to stop Bayer Leverkusen's dominance. Indeed, next season there may be many changes that will occur but still, I personally believe that Bayer Leverkusen still has good abilities to dominate the Bundesliga next season. Moreover,other teams such as Dortmund, Leipzig and maybe several other teams also seem to have good strength to be able to compete strongly in the race for the title next season. Therefore,the Bayern Munich manager really has to be able to manage Bayern Munich well because if not, ofcourse Bayern Munich will be left behind or lose in the title race.