I listen to a lot of music. Eight hours plus per day. It’s become clear to me that having access to a wide variety of music definitely makes the experience of working better than having a single playlist that you listen to again and again. I recommend that you subscribe to one of the streaming music services. The price isn’t too steep, and exploring and building up a library that way is a rewarding endeavour. I put this off for a long time, listening to local albums and “free” music on services like SoundCloud and YouTube, but it is hard to grow a diverse collection that way because as your library grows you need ways of organising and finding your music in one place. In your library you can save whole albums; when trying to concentrate it can be good to listen to lots of similarly themed music, and albums are often a natural division of that. It doesn’t matter if every song isn’t the best song ever, if it’s to help you focus. Or you can build up a custom playlists from those albums instead.
The service I use is Apple Music, which lets you add your own music files to a combined library made up of their songs and yours, which is great as there’s a lot of rarer music which is not available on any streaming service. Other services like Spotify didn’t have this feature last time I checked. It works on Windows and Android as well as Apple devices, and files can be saved offline too.
I could come up with a list of orchestral music, but where to start? I’ve been listening to the Elder Scrolls soundtracks (Morrowind, Oblivion, and Skyrim) today and they never get old. Those are notably absent from your playlist.