How to boost my Bubble App/Website performance?

It’s hard to answer this without seeing your app. A personal plan can get you quite far depending on how your app is designed and what kinds of things you’re trying to do inside of the app. Check out this post on app performance: Performance Q&A guide

A lot of time, boosting app performance comes down to optimizing workflows, limiting the number of searches you’re doing, and so on (again see the linked post above for tips on this from one of the founders of Bubble). If you’re experiencing poor performance, I’d start there before upgrading to a higher tier.