I'm happy to join in writing new songs based on Yasemin's link posted above, otherwise I've had a quick search on the net for some classic, well-known songs that focus on acoustic guitars and vocals, but easy to implement instruments like Cello, Piano, Bass and Percussion:
Mr Big - To Be With You - https://www.youtube.com/watch?v=5QD5n98R_nk
CCR - Have You Ever Seen The Rain? - https://www.youtube.com/watch?v=Gu2pVPWGYMQ
Fleetwood Mac - Landslide - https://www.youtube.com/watch?v=W3cGxlZjMWU
Phil Collins - Another Day In Paradise - https://www.youtube.com/watch?v=Qt2mbGP6vFI
Or perhaps we can even transform a much more different song into something a little more laid-back and acoustic:
Michael Jackson - Rock With You - https://www.youtube.com/watch?v=5X-Mrc2l1d0
Obviously there's thousands more choices, these were just a few that popped up in my mind.
Feel free to shoot through any other ideas, and we can have a quick vote on it soon.
//EDIT - Well this is strange, the website won't allow me to post more than three times in a single topic because I'm a 'new user'? Which means I have to edit an old post.
Anyway, hey @JotPe, I couldn't find your email address on your profile to be added to the shared Dropbox, so I'll just dump it here in hopes you'll see it and add me as well:
I agree with the non-copyrighted music idea, it'd be much more beneficial for all of us to collaborate in creating something new.