However, I also still had an old Mycelium wallet on my previous phone (which is now broken). I have the 12 word seed. Is there any other, perhaps temporary wallet (preferably online) where I can import the seed for my old Mycelium version, so I can send the remaining bitcoins from there to my new wallet?
You don't need anything but Mycelium. You can just use cold storage / offline wallet spending.
You would need to make QR-Code of the old seed, or write it in some text editor and than copy to clipboard.
In the menu of Mycelium (right up corner) should be "Offline wallet", or something like this.
I'm not sure of name because I don't use English in my smartphone.