SharePoint document library can store 30 million files and folders without any problem. You will have to create appropriate folder structures to store the files so that none of them crosses the 5000 list view threshold limitation and you are still able to open the document library and use the associated search box. This is the best option, since, if you use this with modern list experience then the search box in the upper left corner in the modern document library will show you items from all the subfolders under the current folder.
Or, you can create appropriate indexed columns and use them to create filtered views in your document library. In this way, you should be able to see your 'daily used files' whenever you open the document library by default. Now, to find the 'not daily used files', you will have to use SharePoint search (unless you use one of the filtered columns and create your custom view, like, show all items created between 2 dates, which will use 'created' column as filter and you need to create index on that column).
If you are using SharePoint search, then it is possible to indicate a specific document library to show results for. There shouldn't be any performance issues if you use SharePoint search, only the content might take some time to get indexed.