I finally found a way, but not a completely easy one.
I had purchased these on Amazon: https://www.amazon.es/FosPower-Concepti ... B016E5PEXC
These are quite long, but still wouldn't fit. Someone suggested following the advice on a Youtube video, where a guy enlarges the hole to the 3.5 mm socket with a knife, something I wouldn't recommend, since you will loose warranty.
Yesterday I had an idea, and, using a small precision file, I was able to carefully smooth a bit around the lowest part of the connector, in order to remove the bump that would prevent it from going further into the socket. Well, it worked, and I'm now using the adapter perfectly well.
It's not an ideal solution, and sanding metals takes some time, but I can now use some adapters that I had almost discarded.