Use xp ranges, like 0 to 1000 and 2000 to 3000 etc (or a range you like, and process this in your multilayer room name. I.e. range1k, range2k, range3k etc
Then, after connecting and searching for available rooms, show or join rooms which has your range in the room name.
Player is in the 2k range xp, upon start it sets the room name to range2k and auto joins it.
If this happens to all players who are in the 2k range, they will auto join the first available room which starts with range 2k.
Voila .. No extra server needed
Ps if a player levels up after a played game simply update the room name to the new range.
I did a similair thing for countries based room selection where people wanted to join people from the same country. It works.