So, get more hardware, somehow get my phone's memory up to snuff, prepare mp3 lists in advance...by ripping YouTube videos, I guess, and keep them around, as well as playlist files? Yeah, that's easier than just taking someone else's playlist on YouTube and getting the whole CD or whatever in one go.
Thing is, I've found, youtube videos and playlists (especially of music) that you don't manage yourself (and even some you do) have a tendency to vanish at random. My favorites list is chock full of "this video is no longer available" markers.
But once you've got that MP3, you've got it forever (as long as you remember to keep backups in case of catastrophe, naturally). Build yourself a collection over time, and you'll always have what you like, on hand. No internet connection necessary.
And if you're complaining about the cost of bluetooth speakers, I have no sympathy. They're 20 bucks.
Also, also, I refuse to believe your phone can't play MP3s. Phones could do that before there were smartphones.
Also also also, the compression on youtube makes music SUCK. Seriously, it's so bad. It may be a good place to discover music, but the difference between youtube and even a 192kbit MP3, much less a 320kbit one, will bring tears to your eyes. So no, do NOT record your MP3s off youtube. That's a sucker move.