Check this out if it's suites your requirements:

https://www.amazon.com/Voice-Activity-Ltd-Sound-Stream/dp/B08NDD6TWZ

This skill uses your personal Dropbox account to host your audio. You can create unlimited custom playlists. Just read the instructions, it's pretty simple.

Disclaimer: I've build that skill. So, if you have any further questions, let me know.

You're doing an outstanding job, helping other people. All the best.

Hi Odmin, it's already there:
https://www.amazon.com/Voice-Activity-Ltd-Sound-Stream/dp/B08NDD6TWZ

You may try the Sound Stream Alexa skill: https://www.amazon.com/Voice-Activity-Ltd-Sound-Stream/dp/B08NDD6TWZ

It allows you to play your own audio from your personal Dropbox account. Majority of the audio formats are supported, including FLAC.

You can also share playlists across all your Echo devices.

There are fast forward and rewind commands available as well, great for audiobooks.

This quick tutorial may help: https://m.youtube.com/watch?v=_gfLWlKQmwM